Binder composition for non-aqueous secondary battery heat-resistant layer, slurry composition for non-aqueous secondary battery heat-resistant layer, heat-resistant layer for non-aqueous secondary battery, and non-aqueous secondary battery

ABSTRACT

Provided is a binder composition for a non-aqueous secondary battery heat-resistant layer with which it is possible to produce a slurry composition for a non-aqueous secondary battery heat-resistant layer that has excellent dispersion stability and coatability and that can form a heat-resistant layer for a non-aqueous secondary battery having excellent heat shrinkage resistance. The binder composition for a non-aqueous secondary battery heat-resistant layer contains a water-soluble polymer and water. The water-soluble polymer includes an amide group-containing monomer unit, an acid group-containing monomer unit, and a hydroxyl group-containing monomer unit. The proportional content of the amide group-containing monomer unit in the water-soluble polymer is not less than 63 mass % and not more than 98 mass % and the proportional content of the acid group-containing monomer unit in the water-soluble polymer is not less than 1 mass % and not more than 20 mass %.

TECHNICAL FIELD

The present disclosure relates to a binder composition for a non-aqueoussecondary battery heat-resistant layer, a slurry composition for anon-aqueous secondary battery heat-resistant layer, a heat-resistantlayer for a non-aqueous secondary battery, and a non-aqueous secondarybattery.

BACKGROUND

Non-aqueous secondary batteries (hereinafter, also referred to simply as“secondary batteries”) such as lithium ion secondary batteries havecharacteristics such as compact size, light weight, high energy density,and the ability to be repeatedly charged and discharged, and are used ina wide variety of applications. A secondary battery typically includesbattery members such as electrodes (positive electrode and negativeelectrode) and a separator that isolates the positive electrode and thenegative electrode from each other. Battery members that include aprotective layer for improving heat resistance (i.e., a heat-resistantlayer) are conventionally used as such battery members.

A heat-resistant layer of a secondary battery may be a layer that isformed by binding non-conductive inorganic particles such as aluminathrough a binder. Such a heat-resistant layer is normally formed bypreparing a slurry composition (hereinafter, also referred to as a“slurry composition for a non-aqueous secondary battery heat-resistantlayer” or simply as a “slurry composition for a heat-resistant layer”)having non-conductive inorganic particles and a binder dissolved ordispersed in a dispersion medium such as water, and then applying theslurry composition for a heat-resistant layer onto a substrate such as aseparator substrate or electrode substrate and drying the slurrycomposition for a heat-resistant layer.

In recent years, attempts have been made to improve binder compositionsused in heat-resistant layer formation in order to achieve furtherimprovement of secondary battery performance (for example, refer toPatent Literature (PTL) 1).

As one specific example, PTL 1 discloses a binder composition for asecondary battery porous membrane that contains a polycarboxylic acidhaving specific properties and water, and reports that this bindercomposition for a secondary battery porous membrane has highpreservation stability and that a porous membrane for a secondarybattery produced using the binder composition is easy to coat andenables production of a secondary battery having improved performance interms of high-temperature cycle characteristics and the like.

CITATION LIST Patent Literature

PTL 1: WO2015/129408A1

SUMMARY Technical Problem

However, there has been demand for further improvement of secondarybattery performance in recent years, and the conventional bindercomposition described above leaves room for improvement in terms ofimproving dispersion stability of a slurry composition produced usingthe binder composition while also further increasing coatability of theslurry composition. Moreover, it would be desirable to further improvethe heat shrinkage resistance of a heat-resistant layer obtained usingthe conventional binder composition described above.

Accordingly, one object of the present disclosure is to provide a bindercomposition for a non-aqueous secondary battery heat-resistant layerwith which it is possible to produce a slurry composition for anon-aqueous secondary battery heat-resistant layer that has excellentdispersion stability and coatability and that can form a heat-resistantlayer for a non-aqueous secondary battery having excellent heatshrinkage resistance.

Another object of the present disclosure is to provide a slurrycomposition for a non-aqueous secondary battery heat-resistant layerthat has excellent dispersion stability and coatability and that canform a heat-resistant layer for a non-aqueous secondary battery havingexcellent heat shrinkage resistance.

Yet another object of the present disclosure is to provide aheat-resistant layer for a non-aqueous secondary battery that hasexcellent heat shrinkage resistance and a non-aqueous secondary batterythat includes this heat-resistant layer.

Solution to Problem

The inventor conducted diligent investigation with the aim of solvingthe problem set forth above. The inventor discovered that it is possibleto form a slurry composition having excellent dispersion stability andcoatability and a heat-resistant layer having excellent heat shrinkageresistance by using a binder composition containing water and awater-soluble polymer that includes an amide group-containing monomerunit, an acid group-containing monomer unit, and a hydroxylgroup-containing monomer unit and in which the proportional contents ofthe amide group-containing monomer unit and the acid group-containingmonomer unit are within specific ranges. In this manner, the inventorcompleted the present disclosure.

Specifically, the present disclosure aims to advantageously solve theproblem set forth above, and a presently disclosed binder compositionfor a non-aqueous secondary battery heat-resistant layer comprises awater-soluble polymer and water, wherein the water-soluble polymerincludes an amide group-containing monomer unit, an acidgroup-containing monomer unit, and a hydroxyl group-containing monomerunit, and proportional content of the amide group-containing monomerunit in the water-soluble polymer is not less than 63 mass % and notmore than 98 mass % and proportional content of the acidgroup-containing monomer unit in the water-soluble polymer is not lessthan 1 mass % and not more than 20 mass %. Through a binder compositioncontaining water and a water-soluble polymer that includes an amidegroup-containing monomer unit, an acid group-containing monomer unit,and a hydroxyl group-containing monomer unit and in which theproportional contents of the amide group-containing monomer unit and theacid group-containing monomer unit are within the ranges set forth abovein this manner, it is possible to produce a slurry composition that hasexcellent dispersion stability and coatability. Moreover, a slurrycomposition that is produced in this manner enables good formation of aheat-resistant layer having excellent heat shrinkage resistance.

The phrase “includes a monomer unit” as used in relation to a polymer inthe present disclosure means that “a polymer obtained with the monomerincludes a repeating unit derived from the monomer”.

Moreover, the “proportional content (mass %)” of each monomer unit (eachrepeating unit) included in a polymer that is referred to in the presentdisclosure can be measured using a nuclear magnetic resonance (NMR)method such as ¹H-NMR or ¹³C-NMR.

In the presently disclosed binder composition for a non-aqueoussecondary battery heat-resistant layer, proportional content of thehydroxyl group-containing monomer unit in the water-soluble polymer ispreferably not less than 1 mass % and not more than 25 mass %. When theproportional content of the hydroxyl group-containing monomer unit inthe water-soluble polymer is within the range set forth above,dispersion stability and coatability of a slurry composition can befurther improved, and heat shrinkage resistance of a heat-resistantlayer can be even further increased.

In the presently disclosed binder composition for a non-aqueoussecondary battery heat-resistant layer, the hydroxyl group-containingmonomer unit is preferably a hydroxyl group-containing (meth)acrylamidemonomer unit. When the hydroxyl group-containing monomer unit includedin the water-soluble polymer of the binder composition is a hydroxylgroup-containing (meth)acrylamide monomer unit, the amount of waterimported into a secondary battery due to a heat-resistant layer can bereduced while also even further increasing heat shrinkage resistance ofthe heat-resistant layer. In addition, cycle characteristics of thesecondary battery can be improved.

Note that in the present disclosure, “(meth)acryl” is used to indicate“acryl” and/or “methacryl”.

In the presently disclosed binder composition for a non-aqueoussecondary battery heat-resistant layer, a molar ratio of proportionalcontent of the hydroxyl group-containing monomer unit relative toproportional content of the acid group-containing monomer unit in thewater-soluble polymer is preferably 0.70 or more. When the molar ratioof the proportional content of the hydroxyl group-containing monomerunit relative to the proportional content of the acid group-containingmonomer unit in the water-soluble polymer (hereinafter, also referred tosimply as the “hydroxyl group/acid group molar ratio”) is not less thanthe value set forth above, dispersion stability and coatability of aslurry composition can be further improved.

Note that the “hydroxyl group/acid group molar ratio” referred to in thepresent disclosure can be calculated from measurement values that areobtained through measurement of the proportional content (mol %) of theacid group-containing monomer unit and the proportional content (mol %)of the hydroxyl group-containing monomer unit by a nuclear magneticresonance (NMR) method such as ¹H-NMR or ¹³C-NMR.

In the presently disclosed binder composition for a non-aqueoussecondary battery heat-resistant layer, the water-soluble polymerpreferably has a weight-average molecular weight of not less than200,000 and not more than 2,000,000. When the weight-average molecularweight of the water-soluble polymer contained in the binder compositionis within the range set forth above, coatability of a slurry compositioncan be further improved, and heat shrinkage resistance of aheat-resistant layer can be even further increased.

Note that the weight-average molecular weight of a water-soluble polymerreferred to in the present disclosure can be measured by gel permeationchromatography (GPC).

The presently disclosed binder composition for a non-aqueous secondarybattery heat-resistant layer preferably further comprises a particulatepolymer. When the binder composition further contains a particulatepolymer, good close adherence can be achieved between a substrate and aheat-resistant layer that is obtained using the binder composition. Inaddition, a secondary battery can be provided with excellent cyclecharacteristics.

Moreover, the present disclosure aims to advantageously solve theproblem set forth above, and a presently disclosed slurry compositionfor a non-aqueous secondary battery heat-resistant layer comprises:non-conductive inorganic particles; and any one of the bindercompositions for a non-aqueous secondary battery heat-resistant layerset forth above. A slurry composition that contains non-conductiveinorganic particles and any one of the binder compositions set forthabove in this manner has excellent dispersion stability and coatability.Moreover, this slurry composition enables formation of a heat-resistantlayer having excellent heat shrinkage resistance.

Furthermore, the present disclosure aims to advantageously solve theproblem set forth above, and a presently disclosed heat-resistant layerfor a non-aqueous secondary battery is formed using the slurrycomposition for a non-aqueous secondary battery heat-resistant layer setforth above. A heat-resistant layer that is formed from the slurrycomposition set forth above in this manner has excellent heat shrinkageresistance.

Also, the present disclosure aims to advantageously solve the problemset forth above, and a presently disclosed non-aqueous secondary batterycomprises the heat-resistant layer for a non-aqueous secondary batteryset forth above. A secondary battery that includes a battery memberincluding the heat-resistant layer set forth above in this manner hassufficiently ensured safety.

Advantageous Effect

According to the present disclosure, it is possible to provide a bindercomposition for a non-aqueous secondary battery heat-resistant layerwith which it is possible to produce a slurry composition for anon-aqueous secondary battery heat-resistant layer that has excellentdispersion stability and coatability and that can form a heat-resistantlayer for a non-aqueous secondary battery having excellent heatshrinkage resistance.

Moreover, according to the present disclosure, it is possible to providea slurry composition for a non-aqueous secondary battery heat-resistantlayer that has excellent dispersion stability and coatability and thatcan form a heat-resistant layer for a non-aqueous secondary batteryhaving excellent heat shrinkage resistance.

Furthermore, according to the present disclosure, it is possible toprovide a heat-resistant layer for a non-aqueous secondary battery thathas excellent heat shrinkage resistance and a non-aqueous secondarybattery that includes this heat-resistant layer.

DETAILED DESCRIPTION

The following provides a detailed description of embodiments of thepresent disclosure.

The presently disclosed binder composition for a non-aqueous secondarybattery heat-resistant layer can be used in production of the presentlydisclosed slurry composition for a non-aqueous secondary batteryheat-resistant layer. Moreover, the presently disclosed slurrycomposition for a non-aqueous secondary battery heat-resistant layer canbe used in formation of a heat-resistant layer of a non-aqueoussecondary battery such as a lithium ion secondary battery. A feature ofthe presently disclosed heat-resistant layer for a non-aqueous secondarybattery is that it is formed from the presently disclosed slurrycomposition for a non-aqueous secondary battery heat-resistant layer.Moreover, a feature of the presently disclosed non-aqueous secondarybattery is that it includes a heat-resistant layer for a non-aqueoussecondary battery that has been produced using the presently disclosedslurry composition for a non-aqueous secondary battery heat-resistantlayer.

(Binder Composition for Non-Aqueous Secondary Battery Heat-ResistantLayer)

The presently disclosed binder composition contains a water-solublepolymer and water serving as a dispersion medium, and optionally furthercontains a particulate polymer and other components.

Features of the presently disclosed binder composition are that theaforementioned water-soluble polymer includes an amide group-containingmonomer unit, an acid group-containing monomer unit, and a hydroxylgroup-containing monomer unit, that the proportional content of theamide group-containing monomer unit is not less than 63 mass % and notmore than 98 mass %, and that the proportional content of the acidgroup-containing monomer unit is not less than 1 mass % and not morethan 20 mass %.

As a result of the presently disclosed binder composition containing, inwater, a water-soluble polymer that includes an amide group-containingmonomer unit, an acid group-containing monomer unit, and a hydroxylgroup-containing monomer unit and in which the proportional contents ofthe amide group-containing monomer unit and the acid group-containingmonomer unit are within the ranges set forth above, the bindercomposition can be used to produce a slurry composition having excellentdispersion stability and coatability and also to form a heat-resistantlayer having excellent heat shrinkage resistance. Although it is notclear why the effects described above are obtained by using a bindercomposition that has the water-soluble polymer described above dissolvedin water in this manner, the reason for this is presumed to be asfollows.

Firstly, the amide group-containing monomer unit included in thewater-soluble polymer of the binder composition is thought to functionas a main framework for imparting high rigidity to the water-solublepolymer and thereby improving heat shrinkage resistance of an obtainedheat-resistant layer.

Moreover, the acid group-containing monomer unit included in thewater-soluble polymer of the binder composition binds to non-conductiveinorganic particles through electrostatic interactions in a slurry andthereby functions as a site of adsorption to the non-conductiveinorganic particles. However, excessively strong adsorption of an acidgroup-containing monomer unit to non-conductive inorganic particles maycause aggregation of the non-conductive inorganic particles and reducedispersion stability of the non-conductive inorganic particles in theslurry. Such excessive adsorption of an acid group-containing monomerunit to non-conductive inorganic particles can be inhibited hereinthrough a hydration effect of a hydroxyl group because the water-solublepolymer further includes a hydroxyl group-containing monomer unit. It isthought that for this reason, the dispersion stability of non-conductiveinorganic particles in a slurry can be improved.

Moreover, a slurry composition having excellent dispersion stability asdescribed above is thought to have excellent coatability because theslurry composition can be uniformly applied onto a substrate withoutvariation of coating weight and without the formation of defects(streaks, uneven coating, cissing, etc.) in the resultant heat-resistantlayer.

Consequently, the presently disclosed binder composition can be used toobtain a slurry composition having excellent dispersion stability andcoatability. Moreover, a slurry composition that has been produced usingthe presently disclosed binder composition makes it possible to obtain aheat-resistant layer having excellent heat shrinkage resistance.

<Water-Soluble Polymer>

The water-soluble polymer contained in the binder composition for anon-aqueous secondary battery heat-resistant layer is a component that,in a slurry composition, can contribute to improving dispersionstability and coatability of the slurry composition. Moreover, thewater-soluble polymer is a component that can function as a binder in aheat-resistant layer formed using the slurry composition, and can impartadhesiveness to a heat-resistant layer formed using a slurry compositionthat contains the binder composition while also holding non-conductiveinorganic particles contained in the heat-resistant layer so that thenon-conductive inorganic particles do not detach from the heat-resistantlayer.

Note that when a polymer is referred to as “water-soluble” in thepresent disclosure, this means that when 0.5 g of the polymer isdissolved in 100 g of water at a temperature of 25° C., insolublecontent is less than 1.0 mass %.

The water-soluble polymer includes an amide group-containing monomerunit and an acid group-containing monomer unit in proportions that arewithin specific ranges and also includes a hydroxyl group-containingmonomer unit. Note that the water-soluble polymer may include repeatingunits other than the amide group-containing monomer unit, the acidgroup-containing monomer unit, and the hydroxyl group-containing monomerunit (hereinafter, referred to as “other repeating units”).

«Amide Group-Containing Monomer Unit»

Examples of amide group-containing monomers that can form the amidegroup-containing monomer unit include N-vinylacetamide,(meth)acrylamide, dimethyl(meth)acrylamide, diethyl(meth)acrylamide,N-methoxymethyl(meth)acrylamide, anddimethylaminopropyl(meth)acrylamide. Of these amide group-containingmonomers, acrylamide and methacrylamide are preferable from a viewpointof even further increasing heat shrinkage resistance of a heat-resistantlayer, and acrylamide is more preferable. One amide group-containingmonomer may be used individually, or two or more amide group-containingmonomers may be used in combination.

Note that a monomer unit including both an amide group and a hydroxylgroup is considered to be included among the “hydroxyl group-containingmonomer unit” and not be included among the “amide group-containingmonomer unit” in the present disclosure. Moreover, a monomer unitincluding both an amide group and an acid group (carboxy group, sulfogroup, phosphate group, etc.) is considered to be included among the“acid group-containing monomer unit” and not be included among the“amide group-containing monomer unit” in the present disclosure.

When the amount of all repeating units (all monomer units) in thewater-soluble polymer used herein is taken to be 100 mass %, theproportional content of the amide group-containing monomer unit in thewater-soluble polymer is required to be not less than 63 mass % and notmore than 98 mass %, is preferably 67 mass % or more, more preferably 71mass % or more, and even more preferably 74 mass % or more, and ispreferably 95 mass % or less, and more preferably 90 mass % or less.When the proportional content of the amide group-containing monomer unitin the water-soluble polymer is less than 63 mass %, heat shrinkageresistance of a heat-resistant layer cannot be sufficiently ensuredbecause rigidity of the water-soluble polymer decreases. On the otherhand, when the proportional content of the amide group-containingmonomer unit in the water-soluble polymer is more than 98 mass %,dispersion stability of a slurry composition decreases.

«Acid Group-Containing Monomer Unit»

Examples of acid group-containing monomers that can form the acidgroup-containing monomer unit include carboxy group-containing monomers,sulfo group-containing monomers, and phosphate group-containingmonomers. Note that an acid group of the acid group-containing monomerunit may form a salt with an alkali metal, ammonia, or the like.

Examples of carboxy group-containing monomers that can form a carboxygroup-containing monomer unit include monocarboxylic acids, derivativesof monocarboxylic acids, dicarboxylic acids, acid anhydrides ofdicarboxylic acids, and derivatives of dicarboxylic acids and acidanhydrides thereof.

Examples of monocarboxylic acids include acrylic acid, methacrylic acid,and crotonic acid.

Examples of derivatives of monocarboxylic acids include 2-ethylacrylicacid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylicacid, and α-chloro-β-E-methoxyacrylic acid.

Examples of dicarboxylic acids include maleic acid, fumaric acid, anditaconic acid.

Examples of derivatives of dicarboxylic acids include methylmaleic acid,dimethylmaleic acid, phenylmaleic acid, chloromaleic acid,dichloromaleic acid, fluoromaleic acid, and maleic acid monoesters suchas nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, andfluoroalkyl maleates.

Examples of acid anhydrides of dicarboxylic acids include maleicanhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleicanhydride.

An acid anhydride that produces a carboxy group through hydrolysis canalso be used as a carboxy group-containing monomer.

Examples of sulfo group-containing monomers that can form a sulfogroup-containing monomer unit include vinyl sulfonic acid, methyl vinylsulfonic acid, (meth)allyl sulfonic acid, styrene sulfonic acid,(meth)acrylic acid 2-sulfoethyl, 2-acrylamido-2-methylpropane sulfonicacid, and 3-allyloxy-2-hydroxypropane sulfonic acid.

Note that in the present disclosure, “(meth)allyl” is used to indicate“allyl” and/or “methallyl”.

Examples of phosphate group-containing monomers that can form aphosphate group-containing monomer unit include 2-(meth)acryloyloxyethylphosphate, methyl-2-(meth)acryloyloxyethyl phosphate, andethyl-(meth)acryloyloxyethyl phosphate.

Note that in the present disclosure, “(meth)acryloyl” is used toindicate “acryloyl” and/or “methacryloyl”.

One of the acid group-containing monomers described above may be usedindividually, or two or more of the acid group-containing monomersdescribed above may be used in combination. From a viewpoint ofimproving close adherence of a heat-resistant layer and a substrate andalso even further improving coatability of a slurry composition, carboxygroup-containing monomers are preferable, monocarboxylic acids are morepreferable, and acrylic acid is even more preferable as an acidgroup-containing monomer that can form the acid group-containing monomerunit.

When the amount of all repeating units (all monomer units) in thewater-soluble polymer used herein is taken to be 100 mass %, theproportional content of the acid group-containing monomer unit in thewater-soluble polymer is required to be not less than 1 mass % and notmore than 20 mass %, is preferably 2 mass % or more, more preferably 3mass % or more, even more preferably 5 mass % or more, and particularlypreferably 7 mass % or more, and is preferably 16 mass % or less, morepreferably 12 mass % or less, and even more preferably 10 mass % orless. When the proportional content of the acid group-containing monomerunit in the water-soluble polymer is less than 1 mass %, coatability ofa slurry composition decreases. Moreover, close adherence of aheat-resistant layer and a substrate cannot be sufficiently ensuredbecause adsorption strength of the water-soluble polymer tonon-conductive inorganic particles decreases. On the other hand, whenthe proportional content of the acid group-containing monomer unit inthe water-soluble polymer is more than 20 mass %, dispersion stabilityof a slurry composition decreases.

«Hydroxyl Group-Containing Monomer Unit»

Examples of hydroxyl group-containing monomers that can form thehydroxyl group-containing monomer unit include hydroxyl group-containing(meth)acrylamide monomers such as N-hydroxymethylacrylamide,N-hydroxyethylacrylamide, N-hydroxypropylacrylamide,N-hydroxymethylmethacrylamide, N-hydroxyethylmethacrylamide, andN-hydroxypropylmethacrylamide; and hydroxyl group-containing(meth)acrylate monomers such as 2-hydroxymethyl acrylate, 2-hydroxyethylacrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate,2-hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate,2-hydroxypropyl methacrylate, and 2-hydroxybutyl methacrylate.

Of these hydroxyl group-containing monomers, hydroxyl group-containing(meth)acrylamide monomers are preferable from a viewpoint of reducingthe amount of water that is imported into a secondary battery due to aheat-resistant layer and even further increasing heat shrinkageresistance of the heat-resistant layer while also improving cyclecharacteristics of the secondary battery, and N-hydroxyethylacrylamideand N-hydroxymethylacrylamide are more preferable. One hydroxylgroup-containing monomer may be used individually, or two or morehydroxyl group-containing monomers may be used in combination.

Note that in the present disclosure, “(meth)acrylate” is used toindicate “acrylate” and/or “methacrylate”.

The water-soluble polymer contained in the presently disclosed bindercomposition is required to include a hydroxyl group-containing monomerunit. When the water-soluble polymer does not include a hydroxylgroup-containing monomer unit, dispersion stability and coatability of aslurry composition decrease.

When the amount of all repeating units (all monomer units) in thewater-soluble polymer is taken to be 100 mass %, the proportionalcontent of the hydroxyl group-containing monomer unit in thewater-soluble polymer is preferably 1 mass % or more, more preferably 3mass % or more, even more preferably 4 mass % or more, and particularlypreferably 10 mass % or more, and is preferably 25 mass % or less, morepreferably 21 mass % or less, even more preferably 18 mass % or less,and particularly preferably 17 mass % or less. When the proportionalcontent of the hydroxyl group-containing monomer unit in thewater-soluble polymer is 1 mass % or more, dispersion stability andcoatability of a slurry composition can be further improved. On theother hand, when the proportional content of the hydroxylgroup-containing monomer unit in the water-soluble polymer is 25 mass %or less, heat shrinkage resistance of a heat-resistant layer can be evenfurther increased.

«Other Repeating Units»

No specific limitations are placed on other repeating units included inthe water-soluble polymer. For example, the water-soluble polymer mayinclude a monomer unit derived from a known monomer, such as a(meth)acrylic acid ester monomer unit or cross-linkable monomer unitdescribed further below in the “Particulate polymer” section, as anotherrepeating unit. Note that the water-soluble polymer may include one typeof other repeating unit or may include two or more types of otherrepeating units. When all repeating units (all monomer units) includedin the water-soluble polymer are taken to be 100 mass %, theproportional content of other repeating units is preferably 10 mass % orless, more preferably 5 mass % or less, even more preferably 1 mass % orless, and particularly preferably 0 mass %.

«Properties»

[Hydroxyl Group/Acid Group Molar Ratio]

A molar ratio of the proportional content of the hydroxylgroup-containing monomer unit relative to the proportional content ofthe acid group-containing monomer unit in the water-soluble polymer(i.e., the hydroxyl group/acid group molar ratio) is preferably 0.70 ormore, more preferably 0.80 or more, even more preferably 0.90 or more,and particularly preferably 1.00 or more. When the hydroxyl group/acidgroup molar ratio is 0.70 or more, dispersion stability and coatabilityof a slurry composition can be further improved. The upper limit for thehydroxyl group/acid group molar ratio is not specifically limited andcan, for example, be set as 5.00 or less, as 3.00 or less, or as 2.63 orless.

[Weight-Average Molecular Weight]

The weight-average molecular weight of the water-soluble polymer usedherein is preferably 200,000 or more, more preferably 300,000 or more,even more preferably 400,000 or more, and particularly preferably500,000 or more, and is preferably 2,000,000 or less, more preferably1,500,000 or less, and even more preferably 1,000,000 or less. When theweight-average molecular weight of the water-soluble polymer is 200,000or more, heat shrinkage resistance of a heat-resistant layer can be evenfurther increased because rigidity of the water-soluble polymerimproves. On the other hand, when the weight-average molecular weight ofthe water-soluble polymer is 2,000,000 or less, coatability of a slurrycomposition can be further improved because viscosity of the slurrycomposition decreases.

The weight-average molecular weight of the water-soluble polymer can beadjusted by altering the type and amount of a polymerization initiatorand/or polymerization accelerator used in production of thewater-soluble polymer, for example.

The water-soluble polymer contained in the presently disclosed bindercomposition can interact with non-conductive inorganic particles to asuitable degree, which enables good control of the proportion of thewater-soluble polymer that is adsorbed to non-conductive inorganicparticles in a slurry composition produced using the binder composition.Moreover, through good control of the proportion of the water-solublepolymer that is adsorbed to non-conductive inorganic particles,improvement of dispersion stability and coatability of a slurrycomposition and improvement of close adherence of a heat-resistant layerand a substrate are sufficiently achieved. From a viewpoint of furtherimproving dispersion stability and coatability of a slurry compositionwhile also increasing close adherence of a heat-resistant layer and asubstrate, the proportion of the water-soluble polymer that is adsorbedto non-conductive inorganic particles is preferably not less than 10mass % and not more than 60 mass % when all of the water-soluble polymerin a slurry composition is taken to be 100 mass %. The method by whichthe proportion of the water-soluble polymer that is adsorbed tonon-conductive inorganic particles is measured may, for example, be amethod in which the slurry composition is subjected to centrifugalseparation, non-conductive inorganic particles to which thewater-soluble polymer has adsorbed are subsequently caused to sediment,and then the weight loss behavior of the resultant sediment duringheating is analyzed by Tg/DTA to thereby calculate the proportion of thewater-soluble polymer that is adsorbed to the non-conductive inorganicparticles or a method in which the slurry composition is subjected tocentrifugal separation and the concentration of the water-solublepolymer in a supernatant is subsequently quantified to thereby calculatethe proportion of the water-soluble polymer that is adsorbed to thenon-conductive inorganic particles.

«Production Method Of Water-Soluble Polymer»

The water-soluble polymer described above can, for example, be producedby any method among solution polymerization, suspension polymerization,bulk polymerization, emulsion polymerization, and the like without anyspecific limitations. Moreover, the polymerization method may beaddition polymerization such as ionic polymerization, radicalpolymerization, or living radical polymerization. The polymerization maybe carried out with a commonly used polymerization initiator,polymerization accelerator, emulsifier, dispersant, chain transferagent, or the like, and the amount thereof may also be the same ascommonly used. In particular, aqueous solution polymerization usingwater as a polymerization solvent is preferable because a solventremoval operation is not necessary, solvent safety is high, and aproblem of mixing in of surfactant does not arise.

Note that in a case in which water is used as the polymerization solventand the above-described monomer composition is polymerized in water toproduce an aqueous solution containing the water-soluble polymer, the pHof the aqueous solution is preferably adjusted to not lower than 7 andnot higher than 9 after polymerization. This is because it becomeseasier to provide a slurry composition with good viscosity stabilitywhen the obtained aqueous solution is neutralized and adjusted to a pHthat is within the range set forth above.

Examples of polymerization initiators that can be used in production ofthe water-soluble polymer include, without any specific limitations,known polymerization initiators such as sodium persulfate, ammoniumpersulfate, and potassium persulfate. Of these polymerizationinitiators, ammonium persulfate is preferable. One polymerizationinitiator may be used individually, or two or more polymerizationinitiators may be used in combination in a freely selected ratio.

Examples of polymerization accelerators that can be used include,without any specific limitations, known reducing polymerizationaccelerators such as L-ascorbic acid, sodium bisulfite, andtetramethylethylenediamine. Of these polymerization accelerators,L-ascorbic acid is preferable. One polymerization accelerator may beused individually, or two or more polymerization accelerators may beused in combination in a freely selected ratio.

<Particulate Polymer>

The particulate polymer that can optionally be contained in thepresently disclosed binder composition is a component that functions asa binder in the same manner as the water-soluble polymer describedabove. The inclusion of a particulate polymer in the binder compositioncan improve close adherence of an obtained heat-resistant layer and asubstrate. The particulate polymer is water-insoluble particles that areformed of a specific polymer. Note that when particles are referred toas “water-insoluble” in the present disclosure, this means that when 0.5g of the polymer is dissolved in 100 g of water at a temperature of 25°C., insoluble content is 90 mass % or more.

The particulate polymer is not specifically limited so long as it is aparticulate polymer that is water-insoluble and can be dispersed in adispersion medium such as water. For example, a conjugated dienepolymer, a fluoropolymer, or an acrylic polymer can be used as theparticulate polymer. Of these examples, it is preferable to use anacrylic polymer. By using an acrylic polymer as a particulate polymercontained in the binder composition, it is possible to improve closeadherence of a heat-resistant layer and a substrate and also to increaseoxidation resistance of a battery member that includes theheat-resistant layer.

Note that one particulate polymer may be used individually, or two ormore particulate polymers may be used in combination in a freelyselected ratio.

«Conjugated Diene Polymer»

A conjugated diene polymer is a polymer that includes a conjugated dienemonomer unit. Specific examples of conjugated diene polymers include,but are not specifically limited to, copolymers that include an aromaticvinyl monomer unit and an aliphatic conjugated diene monomer unit(styrene-butadiene copolymer (SBR), etc.), butadiene rubber (BR),isoprene rubber, acrylic rubber (NBR) (copolymer including anacrylonitrile unit and a butadiene unit), and hydrogenated products ofany thereof.

«Fluoropolymer»

Specific examples of fluoropolymers include, but are not specificallylimited to, polyvinylidene fluoride (PVdF) and polyvinylidenefluoride-hexafluoropropylene (PVdF-HFP) copolymer.

«Acrylic Polymer»

An acrylic polymer is a polymer that includes a (meth)acrylic acid estermonomer unit. The acrylic polymer may also include repeating units otherthan the (meth)acrylic acid ester monomer unit. Although a hydrophilicgroup-containing monomer unit and a cross-linkable monomer unit arepreferable as such other repeating units, no specific limitations aremade and monomer units other than a (meth)acrylic acid ester monomerunit, a hydrophilic group-containing monomer unit, and a cross-linkablemonomer unit (i.e., other monomer units) may be included.

[(Meth)Acrylic Acid Ester Monomer Unit]

Examples of (meth)acrylic acid ester monomers that can form the(meth)acrylic acid ester monomer unit include acrylic acid alkyl esterssuch as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropylacrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexylacrylate, heptyl acrylate, octyl acrylate, and 2-ethylhexyl acrylate;and methacrylic acid alkyl esters such as methyl methacrylate, ethylmethacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butylmethacrylate, t-butyl methacrylate, pentyl methacrylate, hexylmethacrylate, heptyl methacrylate, octyl methacrylate, and 2 -ethylhexylmethacrylate. One of these (meth)acrylic acid ester monomers may be usedindividually, or two or more of these (meth)acrylic acid ester monomersmay be used in combination. Of these examples, n-butyl acrylate and2-ethylhexyl acrylate are preferable as (meth)acrylic acid estermonomers.

The proportional content of the (meth)acrylic acid ester monomer unit inthe particulate polymer when the amount of all repeating units (allmonomer units) in the particulate polymer is taken to be 100 mass % ispreferably more than 50 mass %, and more preferably 60 mass % or more,and is preferably 99 mass % or less, and more preferably 97 mass % orless.

[Hydrophilic Group-Containing Monomer Unit]

Examples of hydrophilic group-containing monomers that can form thehydrophilic group-containing monomer unit include the “acidgroup-containing monomers” and the “hydroxyl group-containing monomers”that were described in the “Water-soluble polymer” section. One of thesehydrophilic group-containing monomers may be used individually, or twoor more of these hydrophilic group-containing monomers may be used incombination. Of these examples, methacrylic acid is preferable as ahydrophilic group-containing monomer.

The proportional content of the hydrophilic group-containing monomerunit in the particulate polymer when the amount of all repeating units(all monomer units) in the particulate polymer is taken to be 100 mass %is preferably 1 mass % or more, and is preferably 5 mass % or less.

[Cross-Linkable Monomer Unit]

Examples of cross-linkable monomers that can form the cross-linkablemonomer unit include glycidyl methacrylate, allyl glycidyl ether,ethylene glycol dimethacrylate, allyl (meth)acrylate, anddivinylbenzene. One of these cross-linkable monomers may be usedindividually, or two or more of these cross-linkable monomers may beused in combination. Of these examples, allyl glycidyl ether and allylmethacrylate are preferable as cross-linkable monomers.

The proportional content of the cross-linkable monomer unit in theparticulate polymer when the amount of all repeating units (all monomerunits) in the particulate polymer is taken to be 100 mass % ispreferably 1 mass % or more, and is preferably 5 mass % or less.

[Other Monomer Units]

Examples of other monomers that can form other monomer units includemonomers other than the (meth)acrylic acid ester monomers, hydrophilicgroup-containing monomers, and cross-linkable monomers described abovewithout any specific limitations. Specific examples of such othermonomers include α,β-unsaturated nitrile monomers such as acrylonitrileand methacrylonitrile; and styrenic monomers such as styrene,chlorostyrene, vinyltoluene, t-butylstyrene, methyl vinylbenzoate,vinylnaphthalene, chloromethylstyrene, and a-methylstyrene. One of theseother monomers may be used individually, or two or more of these othermonomers may be used in combination. Of these examples, acrylonitrileand styrene are preferable as other monomers.

The proportional content of other monomer units in the particulatepolymer when the amount of all repeating units (all monomer units) inthe particulate polymer is taken to be 100 mass % is preferably 1 mass %or more, and is preferably 35 mass % or less.

«Properties»

[Glass-Transition Temperature]

The glass-transition temperature of the particulate polymer ispreferably lower than 20° C., and more preferably lower than 15° C. Whenthe glass-transition temperature of the particulate polymer is lowerthan 20° C., close adherence of a heat-resistant layer and a substratecan be improved. Moreover, the lower limit for the glass-transitiontemperature of the particulate polymer is not specifically limited andcan be set as higher than −120° C. or as higher than −60° C., forexample.

Note that the “glass-transition temperature” of a particulate polymerreferred to in the present disclosure can be measured by a methoddescribed in the EXAMPLES section of the present specification.

Moreover, the glass-transition temperature of the particulate polymercan be adjusted by altering the type and/or amount of a monomer,polymerization initiator, and/or polymerization accelerator used inproduction of the particulate polymer, for example.

[Volume-Average Particle Diameter]

The volume-average particle diameter of the particulate polymer ispreferably 0.1 μm or more, more preferably 0.15 μm or more, even morepreferably 0.2 μm or more, and particularly preferably 0.31 μm or more,and is preferably 1 μm or less, more preferably 0.8 μm or less, and evenmore preferably 0.5 μm or less. When the volume-average particlediameter of the particulate polymer is 0.1 μm or more, cyclecharacteristics of a secondary battery can be improved. On the otherhand, when the volume-average particle diameter of the particulatepolymer is 1 μm or less, close adherence of a heat-resistant layer and asubstrate can be improved.

Note that the “volume-average particle diameter” referred to in thepresent disclosure is the “particle diameter (D50) at which, in aparticle size distribution (by volume) measured by laser diffraction,cumulative volume calculated from a small diameter end of thedistribution reaches 50%”.

Moreover, the volume-average particle diameter of the particulatepolymer can be adjusted by altering the type and/or amount of a monomer,polymerization initiator, and/or polymerization accelerator used inproduction of the particulate polymer, for example.

«Production Method of Particulate Polymer»

The polymerization method of the particulate polymer is not specificallylimited and may, for example, be any of solution polymerization,suspension polymerization, bulk polymerization, emulsion polymerization,or the like. Moreover, the polymerization reaction may be additionpolymerization such as ionic polymerization, radical polymerization, orliving radical polymerization. The polymerization may be carried outwith a commonly used polymerization solvent, emulsifier, dispersant,polymerization initiator, chain transfer agent, or the like, and theamount thereof may also be the same as commonly used.

Although no specific limitations are placed on the content ratio of thewater-soluble polymer and the particulate polymer in the presentlydisclosed binder composition, the proportion constituted by thewater-soluble polymer among the total content of the water-solublepolymer and the particulate polymer is preferably 15 mass % or more,more preferably 25 mass % or more, and even more preferably 30 mass % ormore, and is preferably 70 mass % or less, more preferably 60 mass % orless, and even more preferably 50 mass % or less. Heat shrinkageresistance of a heat-resistant layer can be further improved when theproportion constituted by the water-soluble polymer among the totalcontent of the water-soluble polymer and the particulate polymer is 15mass % or more, whereas close adherence of a heat-resistant layer and asubstrate can be increased when this proportion is 70 mass % or less.

<Dispersion Medium>

The dispersion medium of the presently disclosed binder composition isnot specifically limited so long as it includes water. For example, thepresently disclosed binder composition may contain just water as thedispersion medium or may contain a mixture of water and an organicsolvent (for example, an ester, ketone, or alcohol) as the dispersionmedium. Note that the presently disclosed binder composition may containone organic solvent or may contain two or more organic solvents.

<Other Components>

Besides the components described above, the presently disclosed bindercomposition may contain reinforcing materials, leveling agents, wettingagents, dispersants, viscosity modifiers, additives for electrolytesolution, preservatives, fungicides, defoamers, polymerizationinhibitors, and binders other than the water-soluble polymer and theparticulate polymer according to the present disclosure. Commonly knownexamples of such components can be used without any specific limitationsso long as they do not affect battery reactions. One other component maybe used individually, or two or more other components may be used incombination in a freely selected ratio.

Examples of wetting agents that can be used include, but are notspecifically limited to, ethylene oxide/propylene oxide surfactants(EO/PO surfactants), fluorine-containing surfactants, silicon-containingsurfactants, and so forth. Of these wetting agents, EO/PO surfactantsand fluorine-containing surfactants are preferable, and EO/POsurfactants are more preferable.

Examples of dispersants that can be used include, but are notspecifically limited to, polycarboxylic acids such as polyacrylic acid,sodium polycarboxylates such as sodium polyacrylate, ammoniumpolycarboxylates such as ammonium polyacrylate, polycarboxylicacid-sulfonic acid copolymers, sodium polycarboxylate-sulfonatecopolymers, and ammonium polycarboxylate-sulfonate copolymers. Of thesedispersants, sodium polyacrylate is preferable.

Specific examples of other components besides the wetting agents anddispersants described above include, but are not specifically limitedto, those described in WO2012/115096A1, for example.

<Production of Binder Composition for Non-Aqueous Secondary BatteryHeat-Resistant Layer>

The presently disclosed binder composition can be produced by using aknown method to mix the previously described water-soluble polymer andwater, and also the particulate polymer and other components that areoptionally used. Specifically, the binder composition can be produced bymixing the above-described components using a mixer such as a ball mill,a sand mill, a bead mill, a pigment disperser, a grinding machine, anultrasonic disperser, a homogenizer, a planetary mixer, or a FILMIX.

Note that in a case in which the water-soluble polymer or the optionalparticulate polymer is produced through polymerization in an aqueoussolvent, the water-soluble polymer or particulate polymer may be mixedwhile still in the form of an aqueous solution or water dispersion so asto produce the binder composition containing water as a solvent.

Moreover, the optional particulate polymer may be added after mixing ofthe water-soluble polymer and non-conductive inorganic particles, forexample, such that production of the binder composition and productionof the subsequently described slurry composition are implemented at thesame time.

(Slurry Composition for Non-Aqueous Secondary Battery Heat-ResistantLayer)

The presently disclosed slurry composition is a composition that is foruse in forming a heat-resistant layer, that contains non-conductiveinorganic particles and the binder composition set forth above, and thatoptionally further contains other components. In other words, thepresently disclosed slurry composition normally contains non-conductiveinorganic particles, a water-soluble polymer, and water serving as adispersion medium, and optionally further contains a particulate polymerand other components. As a result of containing the binder compositionset forth above, the presently disclosed slurry composition hasexcellent dispersion stability and coatability, and enables formation ofa heat-resistant layer having excellent heat shrinkage resistancethrough drying thereof on a substrate.

<Non-Conductive Inorganic Particles>

The non-conductive inorganic particles contained in the slurrycomposition for a heat-resistant layer are not specifically limited solong as they are particles formed of an inorganic material that iselectrochemically stable and is stably present in the environment of useof a secondary battery. Examples of non-conductive inorganic particlesthat are preferable from such a viewpoint include particles of inorganicoxides such as aluminum oxide (alumina, Al₂O₃), hydrous aluminum oxide(boehmite, AlOOH), gibbsite (Al(OH)₃), silicon oxide, magnesium oxide(magnesia), magnesium hydroxide, calcium oxide, titanium oxide(titania), barium titanate (BaTiO₃), ZrO, and alumina-silica complexoxide; particles of nitrides such as aluminum nitride and boron nitride;particles of covalently bonded crystals such as silicon and diamond;particles of sparingly soluble ionic crystals such as barium sulfate,calcium fluoride, and barium fluoride; and fine particles of clays suchas talc and montmorillonite. Of these examples, particles formed ofalumina (alumina particles), particles formed of boehmite (boehmiteparticles), and particles formed of barium sulfate (barium sulfateparticles) are preferable as the non-conductive inorganic particles froma viewpoint of causing good adsorption of the water-soluble polymer andthe particulate polymer and improving close adherence of aheat-resistant layer and a substrate, and alumina particles and bariumsulfate particles are more preferable as the non-conductive inorganicparticles.

These particles may be subjected to element substitution, surfacetreatment, solid solution treatment, or the like as necessary. One ofthese types of particles may be used individually, or two or more ofthese types of particles may be used in combination.

<Binder Composition>

The binder composition is the presently disclosed binder composition setforth above, which contains a water-soluble polymer, water, and anoptional particulate polymer and other components.

The content of the specific water-soluble polymer described above in theslurry composition is preferably 0.5 parts by mass or more, and morepreferably 1 part by mass or more in terms of solid content per 100parts by mass of the non-conductive inorganic particles from a viewpointof even further increasing heat shrinkage resistance of a heat-resistantlayer. Moreover, the content of the water-soluble polymer in the slurrycomposition is preferably 5 parts by mass or less, and more preferably 3parts by mass or less in terms of solid content per 100 parts by mass ofthe non-conductive inorganic particles from a viewpoint of improvingcycle characteristics of a secondary battery.

Furthermore, the content of the previously described particulate polymerin the slurry composition is preferably 1 part by mass or more, morepreferably 1.2 parts by mass or more, and even more preferably 1.4 partsby mass or more in terms of solid content per 100 parts by mass of thenon-conductive inorganic particles from a viewpoint of improving closeadherence of a heat-resistant layer and a substrate. Also, the contentof the particulate polymer in the slurry composition is preferably 20parts by mass or less, more preferably 10 parts by mass or less, andeven more preferably 7 parts by mass or less in terms of solid contentper 100 parts by mass of the non-conductive inorganic particles from aviewpoint of improving cycle characteristics of a secondary battery.

<Other Components>

Examples of other components that may be contained in the slurrycomposition include, but are not specifically limited to, the same othercomponents as may be contained in the presently disclosed bindercomposition.

One other component may be used individually, or two or more othercomponents may be used in combination in a freely selected ratio.

The content of the previously described wetting agent in the slurrycomposition is preferably 0.01 parts by mass or more, more preferably0.05 parts by mass or more, and even more preferably 0.1 parts by massor more per 100 parts by mass of the non-conductive inorganic particles,and is preferably 5 parts by mass or less, more preferably 3 parts bymass or less, and even more preferably 1 part by mass or less per 100parts by mass of the non-conductive inorganic particles. When thecontent of the wetting agent is 0.01 parts by mass or more per 100 partsby mass of the non-conductive inorganic particles, wettability withrespect to a substrate improves, and cissing is inhibited, which makesit possible to even further increase coatability of the slurrycomposition. Moreover, when the content of the wetting agent is 5 partsby mass or less per 100 parts by mass of the non-conductive inorganicparticles, cycle characteristics of a secondary battery can be improved.

The content of the previously described dispersant in the slurrycomposition is preferably 0.1 parts by mass or more, more preferably 0.2parts by mass or more, and even more preferably 0.3 parts by mass ormore per 100 parts by mass of the non-conductive inorganic particles,and is preferably 5 parts by mass or less, more preferably 3 parts bymass or less, and even more preferably 1 part by mass of less per 100parts by mass of the non-conductive inorganic particles. When thecontent of the dispersant is 0.1 parts by mass or more per 100 parts bymass of the non-conductive inorganic particles, dispersion stability ofthe slurry composition can be further improved, and heat shrinkageresistance of a heat-resistant layer can be even further increased.

Moreover, when the content of the dispersant is 5 parts by mass or lessper 100 parts by mass of the non-conductive inorganic particles, theamount of water remaining in a heat-resistant layer formed using theslurry composition can be reduced, and cycle characteristics of asecondary battery can be improved.

<Production of Slurry Composition for Non-Aqueous Secondary BatteryHeat-Resistant Layer>

The slurry composition set forth above can be produced by mixing theabove-described components by a known mixing method. This mixing can beperformed using a mixer such as a ball mill, a sand mill, a bead mill, apigment disperser, a grinding machine, an ultrasonic disperser, ahomogenizer, a planetary mixer, or a FILMIX, for example.

(Heat-Resistant Layer for Non-Aqueous Secondary Battery)

The presently disclosed heat-resistant layer is a layer that is formedfrom the presently disclosed slurry composition set forth above. Forexample, the presently disclosed heat-resistant layer can be formed byapplying the slurry composition set forth above onto the surface of asuitable substrate to form a coating film, and subsequently drying thecoating film that has been formed. In other words, the presentlydisclosed heat-resistant layer is formed of a dried product of theslurry composition set forth above and normally contains at leastnon-conductive inorganic particles and a water-soluble polymer. Notethat components contained in the heat-resistant layer are componentsthat were contained in the slurry composition set forth above, and thepreferred ratio of these components is the same as the preferred ratioof the components in the slurry composition.

The presently disclosed heat-resistant layer has excellent heatshrinkage resistance as a result of being formed from the presentlydisclosed slurry composition containing the presently disclosed bindercomposition.

<Substrate>

No limitations are placed on the substrate onto which the slurrycomposition is applied. For example, a coating film of the slurrycomposition may be formed on the surface of a releasable substrate, thiscoating film may be dried to form a heat-resistant layer, and then thereleasable substrate may be peeled from the heat-resistant layer. Theheat-resistant layer that is peeled from the releasable substrate inthis manner can be used as a free-standing film in formation of abattery member of a secondary battery.

However, it is preferable that a separator substrate or an electrodesubstrate is used as the substrate from a viewpoint of raising batterymember production efficiency since a step of peeling the heat-resistantlayer can be omitted. Specifically, the slurry composition is preferablyapplied onto a separator substrate or an electrode substrate.

«Separator Substrate»

The separator substrate is not specifically limited and may be a knownseparator substrate such as an organic separator substrate. The organicseparator substrate is a porous member that is made from an organicmaterial.

The organic separator substrate may, for example, be a microporousmembrane or non-woven fabric containing a polyolefin resin such aspolyethylene or polypropylene, an aromatic polyamide resin, or the like,and is preferably a microporous membrane or non-woven fabric made frompolyethylene due to the excellent strength thereof.

«Electrode Substrate»

The electrode substrate (positive electrode substrate or negativeelectrode substrate) is not specifically limited and may, for example,be an electrode substrate obtained by forming an electrode mixedmaterial layer containing an electrode active material and a binder on acurrent collector.

The current collector, the electrode active material (positive electrodeactive material or negative electrode active material) and the binderfor an electrode mixed material layer (binder for a positive electrodemixed material layer or binder for a negative electrode mixed materiallayer) in the electrode mixed material layer, and the method by whichthe electrode mixed material layer is formed on the current collectorcan be known examples thereof such as any of those described inJP2013-145763A, for example.

<Formation Method of Heat-Resistant Layer>

Examples of methods by which the heat-resistant layer may be formed on asubstrate such as the separator substrate or the electrode substratedescribed above include:

(1) a method in which the presently disclosed slurry composition isapplied onto the surface of the substrate (surface at the electrodemixed material layer-side in the case of the electrode substrate; sameapplies below) and is then dried;

(2) a method in which the substrate is immersed in the presentlydisclosed slurry composition and is then dried; and

(3) a method in which the presently disclosed slurry composition isapplied onto a releasable substrate and is dried to produce aheat-resistant layer that is then transferred onto the surface of thesubstrate.

Of these methods, method (1) is particularly preferable since it allowssimple control of the thickness of the heat-resistant layer. In moredetail, method (1) includes a step of applying the slurry compositiononto the substrate (application step) and a step of drying the slurrycomposition that has been applied onto the substrate to form aheat-resistant layer (drying step).

«Application Step»

Examples of methods by which the slurry composition can be applied ontothe substrate in the application step include, but are not specificallylimited to, doctor blading, reverse roll coating, direct roll coating,gravure coating, extrusion coating, and brush coating.

«Drying Step»

The method by which the slurry composition on the substrate is dried inthe drying step may be a commonly known method without any specificlimitations. Examples of drying methods that may be used include dryingby warm, hot, or low-humidity air, drying in a vacuum, and dryingthrough irradiation with infrared light, electron beams, or the like.

(Non-Aqueous Secondary Battery)

The presently disclosed secondary battery includes the presentlydisclosed heat-resistant layer set forth above. More specifically, thepresently disclosed secondary battery includes a positive electrode, anegative electrode, a separator, and an electrolyte solution, and hasthe heat-resistant layer set forth above included in at least onebattery member among the positive electrode, the negative electrode, andthe separator.

<Positive Electrode, Negative Electrode, and Separator>

At least one of the positive electrode, the negative electrode, and theseparator used in the presently disclosed secondary battery is a batterymember that includes the presently disclosed heat-resistant layer setforth above. Note that any known positive electrode, negative electrode,or separator can be used without any specific limitations as a positiveelectrode, negative electrode, or separator that does not include thepresently disclosed heat-resistant layer.

<Electrolyte Solution>

The electrolyte solution is normally an organic electrolyte solutionobtained by dissolving a supporting electrolyte in an organic solvent.The supporting electrolyte may, for example, be a lithium salt in thecase of a lithium ion secondary battery. Examples of lithium salts thatcan be used include LiPF₆, LiAsF₆, LiBF₄, LiSbF₆, LiAlCl₄, LiClO₄,CF₃SO₃Li, C₄F₉SO₃Li, CF₃COOLi, (CF₃CO)₂NLi, (CF₃SO₂)₂NLi, and(C₂F₅SO₂)NLi. Of these lithium salts, LiPF₆, LiClO₄, and CF₃SO₃Li arepreferable as they readily dissolve in solvents and exhibit a highdegree of dissociation. One electrolyte may be used individually, or twoor more electrolytes may be used in combination. In general, lithium ionconductivity tends to increase when a supporting electrolyte having ahigh degree of dissociation is used. Therefore, lithium ion conductivitycan be adjusted through the type of supporting electrolyte that is used.

The organic solvent used in the electrolyte solution is not specificallylimited so long as the supporting electrolyte can dissolve therein.Examples of organic solvents that can suitably be used in a lithium ionsecondary battery, for example, include carbonates such as dimethylcarbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC),propylene carbonate (PC), butylene carbonate (BC), and ethyl methylcarbonate (EMC); esters such as γ-butyrolactone and methyl formate;ethers such as 1,2-dimethoxyethane and tetrahydrofuran; andsulfur-containing compounds such as sulfolane and dimethyl sulfoxide.Furthermore, a mixture of such solvents may be used. Of these solvents,carbonates are preferable due to having high permittivity and a widestable potential region.

The concentration of the electrolyte in the electrolyte solution may beadjusted as appropriate. Furthermore, known additives may be added tothe electrolyte solution.

<Production Method of Non-Aqueous Secondary Battery>

The presently disclosed non-aqueous secondary battery may be produced,for example, by stacking the positive electrode and the negativeelectrode with the separator in-between, performing rolling, folding, orthe like of the resultant laminate as necessary in accordance with thebattery shape, placing the laminate in a battery container, injectingthe electrolyte solution into the battery container, and sealing thebattery container. Note that at least one member among the positiveelectrode, the negative electrode, and the separator is a member that isequipped with a heat-resistant layer. In order to prevent pressureincrease inside the secondary battery and occurrence of overcharging oroverdischarging, an overcurrent preventing device such as a fuse or aPTC device; an expanded metal; or a lead plate may be provided asnecessary. The shape of the secondary battery may be a coin type, buttontype, sheet type, cylinder type, prismatic type, flat type, or the like.

EXAMPLES

The following provides a more specific description of the presentdisclosure based on examples. However, the present disclosure is notlimited to the following examples. In the following description, “%” and“parts” used in expressing quantities are by mass, unless otherwisespecified.

Moreover, in the case of a polymer that is produced throughpolymerization of a plurality of types of monomers, the proportion inthe polymer constituted by a monomer unit that is formed throughpolymerization of a given monomer is normally, unless otherwisespecified, the same as the ratio (charging ratio) of the given monomeramong all monomers used in polymerization of the polymer. In theexamples and comparative examples, the following methods were used toevaluate the weight-average molecular weight of a water-soluble polymer,the glass-transition temperature and volume-average particle diameter ofa particulate polymer, the dispersion stability and coatability of aslurry composition for a heat-resistant layer, the heat shrinkageresistance of a heat-resistant layer, the close adherence of aheat-resistant layer and a substrate, and the cycle characteristics of asecondary battery.

<Weight-Average Molecular Weight of Water-Soluble Polymer>

An aqueous solution containing a water-soluble polymer that was producedin each example or comparative example was diluted so as to adjust theconcentration thereof to 0.5%. Next, caustic soda was added until the pHreached 10 to 12, 1 hour of immersion was performed in a hot water bathof 80° C. or higher, and then dilution to 0.025% was performed with theeluent indicated below so as to produce a sample. The sample wasanalyzed by gel permeation chromatography under the following conditionsin order to determine the weight-average molecular weight of thewater-soluble polymer.

Apparatus: Gel permeation chromatograph GPC (device No. GPC-26)

Detector: Differential refractive index detector RI (produced by ShowaDenko K.K.; product name: RI-201; sensitivity: 32)

Column: TSKgel GMPWXL×2 (Ø7.8 mm×30 cm; produced by Tosoh Corporation)

Eluent: 0.1 M Tris buffer solution (pH 9; 0.1 M potassium chlorideadded)

Flow rate: 0.7 mL/min

Column temperature: 40° C.

Injection volume: 0.2 mL

Reference sample: Monodisperse polyethylene oxide (PEO) and polyethyleneglycol (PEG) produced by Tosoh Corporation and Sigma-Aldrich

<Glass-Transition Temperature of Particulate Polymer>

A powdered sample obtained by drying a water dispersion containing aparticulate polymer at a temperature of 25° C. for 48 hours was used asa measurement sample. After weighing 10 mg of the measurement sampleinto an aluminum pan, measurement was implemented under conditionsprescribed in JIS Z8703 using a differential scanning calorimeter(produced by SII NanoTechnology Inc.; product name: EXSTAR DSC6220) andwith a measurement temperature range of −100° C. to 200° C. and aheating rate of 20° C./min to obtain a differential scanning calorimetry(DSC) curve. Note that an empty aluminum pan was used as a reference.The temperature at which a derivative signal (DDSC) exhibited a peak inthe heating process was taken to be the glass-transition temperature (°C.). Note that since multiple peaks were measured, the temperature atwhich a peak having large displacement was exhibited was taken to be theglass-transition temperature of the particulate polymer.

<Volume-Average Particle Diameter of Particulate Polymer>

The volume-average particle diameter of a particulate polymer wasmeasured by laser diffraction. Specifically, a produced water dispersioncontaining the particulate polymer (adjusted to a solid contentconcentration of 0.1 mass %) was used as a sample. In a particlediameter distribution (by volume) measured using a laser diffractionparticle size analyzer (produced by

Beckman Coulter Inc.; product name: LS-13 320), the particle diameterD50 at which cumulative volume calculated from a small diameter end ofthe distribution reached 50% was taken to be the volume-average particlediameter.

<Dispersion Stability of Slurry Composition for Heat-Resistant Layer>

After loading 1 kg of a slurry composition for a heat-resistant layerproduced in each example or comparative example into a 1 L plasticbottle, the plastic bottle was left at rest for 10 days. A Mix Rotor wasthen used to perform stirring of the entire plastic bottle that had beenleft at rest. After this stirring, the slurry composition for aheat-resistant layer inside the plastic bottle was sampled at within 1cm of the top, and the solid content concentration of the sampledsupernatant was measured. The slurry composition in the plastic bottleafter stirring was withdrawn from the bottle, and occurrence of adhesionto the bottom of the plastic bottle was checked and was evaluated asfollows.

A: Solid content concentration of supernatant after stirring of 39.5% ormore and no adhesion to bottom of plastic bottle

B: Solid content concentration of supernatant after stirring of 39.5% ormore but adhesion to bottom of plastic bottle observed

C: Solid content concentration of supernatant after stirring of lessthan 39.5%

<Coatability of Slurry Composition for Heat-Resistant Layer>

The external appearance of a heat-resistant layer formed from a slurrycomposition for a heat-resistant layer produced in each example orcomparative example was visually observed and was evaluated as follows.

A: Range over which aggregates, streaks, and/or cissing are not observedis 30 cm×30 cm or more

B: Range over which aggregates, streaks, and/or cissing are not observedis not less than 10 cm×10 cm and less than 30 cm×30 cm

C: Range over which aggregates, streaks, and/or cissing are not observedis less than 10 cm×10 cm

<Heat Shrinkage Resistance of Heat-Resistant Layer>

A heat-resistant layer-equipped separator produced in each example orcomparative example was cut out as a square of 12 cm in width by 12 cmin length, and a square having a side length of 10 cm was drawn in aninner part of the cut out square to obtain a test specimen. The testspecimen was placed inside a 150° C. thermostatic tank and was left for1 hour. Thereafter, the area change of the square drawn in the innerpart (={(area of square before being left−area of square after beingleft)/area of square before being left}×100%) was determined as the heatshrinkage rate and was evaluated by the following standard. A smallerheat shrinkage rate indicates that a heat-resistant layer has betterheat shrinkage resistance.

A: Heat shrinkage rate of less than 10%

B: Heat shrinkage rate of not less than 10% and less than 20%

C: Heat shrinkage rate of 20% or more

<Close Adherence of Heat-Resistant Layer and Substrate>

A heat-resistant layer-equipped separator produced in each example orcomparative example was cut out as 10 mm in width by 50 mm in length toobtain a test specimen. Next, an SUS plate having double-sided tape (No.5608 produced by Nitto Denko Corporation) affixed thereto was prepared,and the surface of the heat-resistant layer of the test specimen wasaffixed to the double-sided tape. One end of the separator substrate waspulled and peeled off at a speed of 50 mm/min such that the peeling facewas at 180°, and the strength when the separator substrate was peeledoff was measured. A higher peel strength indicates better closeadherence of a heat-resistant layer and a substrate.

A: Peel strength of 60 N/m or more

B: Peel strength of not less than 30 N/m and less than 60 N/m

C: Peel strength of less than 30 N/m

<Cycle Characteristics of Secondary Battery>

A lithium ion secondary battery produced in each example or comparativeexample was left at rest in a 25° C. environment for 24 hours.Thereafter, the lithium ion secondary battery was subjected to acharge/discharge operation of charging to 4.2 V (cut-off condition:0.02C) by a constant current-constant voltage (CC-CV) method at a chargerate of 1C and then discharging to 3.0 V by a constant current (CC)method at a discharge rate of 1C, and the initial capacity C0 wasmeasured.

The lithium ion secondary battery was repeatedly subjected to the samecharge/discharge operation in a 25° C. environment, and the capacity Clafter 300 cycles was measured. The capacity maintenance rate AC(=(C1/C0)×100(%)) was calculated and was evaluated by the followingstandard. A higher capacity maintenance rate indicates a smallerdecrease of discharge capacity, and thus indicates better cyclecharacteristics.

A: Capacity maintenance rate AC of 85% or more

B: Capacity maintenance rate AC of not less than 75% and less than 85%

C: Capacity maintenance rate AC of less than 75%

Example 1 <Production of Aqueous Solution Containing Water-SolublePolymer>

A 10 L septum-equipped flask was charged with 6,335 g of deionized waterand 190 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator. These materials were heated to a temperatureof 40° C., and the inside of the flask was purged with nitrogen gas at aflow rate of 100 mL/min. Next, 939.8 g (74.0%) of acrylamide as an amidegroup-containing monomer, 127.0 g (10.0%) of acrylic acid as an acidgroup-containing monomer, and 203.2 g (16.0%) ofN-hydroxyethylacrylamide as a hydroxyl group-containing monomer weremixed and were then injected into the flask by a syringe. Thereafter,200 g of a 5.0% aqueous solution of ammonium persulfate as apolymerization initiator was added into the flask by a syringe, and thereaction temperature was set to 60° C. Once 2 hours had passed, 100 g ofa 5.0% aqueous solution of ammonium persulfate as a polymerizationinitiator and 95 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator were added in order to further raise thereaction conversion rate. Once a further 2 hours had passed, 100 g of a5.0% aqueous solution of ammonium persulfate as a polymerizationinitiator and 95 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator were added. Two hours later, 34 g of a 5%aqueous solution of sodium nitrite as a reaction inhibitor was addedinto the flask and was stirred. Thereafter, the flask was cooled to 40°C. and was converted to an air atmosphere. The pH of the system wasadjusted to 8.0 using 8% lithium hydroxide aqueous solution to therebyyield an aqueous solution containing a water-soluble polymer. Theweight-average molecular weight of the obtained water-soluble polymerwas measured. The result is shown in Table 1.

<Production of Water Dispersion Containing Particulate Polymer>

A reactor including a stirrer was supplied with 70 parts of deionizedwater, 0.15 parts of sodium lauryl sulfate (produced by Kao Corporation;product name: EMAL® 2F (EMAL is a registered trademark in Japan, othercountries, or both)) as an emulsifier, and 0.5 parts of ammoniumpersulfate, the gas phase was purged with nitrogen gas, and thetemperature was raised to 60° C.

Meanwhile, a monomer composition was obtained in a separate vessel bymixing 50 parts of deionized water, 0.5 parts of sodiumdodecylbenzenesulfonate, 94.2 parts of n-butyl acrylate as a(meth)acrylic acid ester monomer, 2 parts of methacrylic acid as ahydrophilic group-containing monomer, 0.3 parts of allyl methacrylateand 1.5 parts of allyl glycidyl ether as cross-linkable monomers, and 2parts of acrylonitrile as another monomer. The monomer composition wascontinuously added into the reactor over 4 hours to carry outpolymerization. The reaction was carried out at 60° C. during theaddition. Once the addition was complete, a further 3 hours of stirringwas performed at 70° C. to complete the reaction and thereby yield awater dispersion containing a particulate polymer.

The glass-transition temperature and the volume-average particlediameter of the obtained particulate polymer were measured. The resultsare shown in Table 1.

<Production of Slurry Composition for Non-Aqueous Secondary BatteryHeat-Resistant Layer>

Alumina particles (produced by Nippon Light Metal Co., Ltd.; productname: LS-256; volume-average particle diameter: 0.5 μm) were prepared asnon-conductive inorganic particles, and sodium polyacrylate (produced byToagosei Co., Ltd.; product name: ARON T-50) was prepared as adispersant.

A dispersion liquid was obtained by mixing 100 parts of thenon-conductive inorganic particles, 0.5 parts of the dispersant, anddeionized water, and then treating the mixture for 1 hour using a beadmill (produced by Ashizawa Finetech Ltd.; product name: LMZ015). Inaddition, 2 parts of solid content of the aqueous solution containingthe water-soluble polymer obtained as described above, 4 parts of solidcontent of the water dispersion containing the particulate polymerobtained as described above, and 0.3 parts of an ethyleneoxide/propylene oxide surfactant (produced by San Nopco Limited; productname: NOPTECHS ED-052) as a wetting agent were mixed so as to produce aslurry composition for a heat-resistant layer having a solid contentconcentration of 40%. Note that this slurry composition for aheat-resistant layer contained a binder composition for a heat-resistantlayer. In other words, production of a slurry composition for aheat-resistant layer and production of a binder composition for aheat-resistant layer were performed at the same time in this example.

The dispersion stability and coatability of the slurry composition for aheat-resistant layer obtained in this manner were evaluated. The resultsare shown in Table 1.

<Production of Separator>

A separator substrate made of polyethylene (produced by Asahi KaseiCorporation; product name: ND412; thickness: 12 μm) was prepared. Theslurry composition for a heat-resistant layer produced as describedabove was applied onto the surface of the prepared separator substrateand was dried at a temperature of 50° C. for 3 minutes to obtain aseparator including a heat-resistant layer at one side (heat-resistantlayer thickness: 2.5 μm).

The heat shrinkage resistance of the heat-resistant layer obtained inthis manner and also the close adherence of the heat-resistant layer andthe separator substrate were evaluated. The results are shown in Table1.

<Formation of Negative Electrode>

A 5 MPa pressure-resistant vessel equipped with a stirrer was chargedwith 33 parts of 1,3-butadiene as an aliphatic conjugated diene monomer,3.5 parts of itaconic acid as a carboxy group-containing monomer, 63.5parts of styrene as an aromatic vinyl monomer, 0.4 parts of sodiumdodecylbenzenesulfonate as an emulsifier, 150 parts of deionized water,and 0.5 parts of potassium persulfate as a polymerization initiator.These materials were sufficiently stirred and were then heated to 50° C.to initiate polymerization. The polymerization reaction was quenched bycooling at the point at which the polymerization conversion rate reached96% to yield a mixture containing a particulate binder(styrene-butadiene copolymer). The mixture was adjusted to pH 8 throughaddition of 5% sodium hydroxide aqueous solution and was then subjectedto thermal-vacuum distillation to remove unreacted monomer. Thereafter,the mixture was cooled to 30° C. or lower to yield a water dispersioncontaining a binder for a negative electrode. A planetary mixer wascharged with 48.75 parts of artificial graphite (theoretical capacity:360 mAh/g) and 48.75 parts of natural graphite (theoretical capacity:360 mAh/g) as negative electrode active materials and 1 part (in termsof solid content) of carboxymethyl cellulose as a thickener. Thesematerials were diluted to a solid content concentration of 60% withdeionized water and were subsequently kneaded at a rotation speed of 45rpm for 60 minutes. Thereafter, 1.5 parts in terms of solid content ofthe water dispersion containing the binder for a negative electrodeobtained as described above was added and was kneaded therewith at arotation speed of 40 rpm for 40 minutes. The viscosity was then adjustedto 3,000±500 mPas (measured by B-type viscometer at 25° C. and 60 rpm)with deionized water to produce a slurry composition for a negativeelectrode mixed material layer.

The slurry composition for a negative electrode mixed material layer wasapplied onto the surface of copper foil of 15 μm in thickness serving asa current collector by a comma coater such as to have a coating weightof 11±0.5 mg/cm². The copper foil having the slurry composition for anegative electrode mixed material layer applied thereon was subsequentlyconveyed inside an oven having a temperature of 80° C. for 2 minutes andan oven having a temperature of 110° C. for 2 minutes at a speed of 400mm/min so as to dry the slurry composition on the copper foil andthereby obtain a negative electrode web having a negative electrodemixed material layer formed on the current collector.

Thereafter, the negative electrode mixed material layer-side of theproduced negative electrode web was roll pressed with a line pressure of11 t (tons) in an environment having a temperature of 25±3° C. to obtaina negative electrode having a negative electrode mixed material layerdensity of 1.60 g/cm³. The negative electrode was subsequently left inan environment having a temperature of 25±3° C. and a relative humidityof 50±5% for 1 week.

<Formation of Positive Electrode>

A slurry composition for a positive electrode mixed material layer wasproduced by loading 96 parts of an active material NMC111(LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂) based on a lithium complex oxide ofCo—Ni—Mn as a positive electrode active material, 2 parts of acetyleneblack (produced by Denka Company Limited; product name HS-100) as aconductive material, and 2 parts of polyvinylidene fluoride (produced byKureha Corporation; product name: KF-1100) as a binder for a positiveelectrode into a planetary mixer, further adding N-methyl-2-pyrrolidone(NMP) as a dispersion medium to adjust the total solid contentconcentration to 67%, and mixing these materials.

Next, the obtained slurry composition for a positive electrode mixedmaterial layer was applied onto aluminum foil of 20 μm in thicknessserving as a current collector by a comma coater such as to have acoating weight of 20±0.5 mg/cm².

The aluminum foil was conveyed inside an oven having a temperature of90° C. for 2 minutes and an oven having a temperature of 120° C. for 2minutes at a speed of 200 mm/min so as to dry the slurry composition onthe aluminum foil and thereby obtain a positive electrode web having apositive electrode mixed material layer formed on the current collector.

Thereafter, the positive electrode mixed material layer-side of theproduced positive electrode web was roll pressed with a line pressure of14 t (tons) in an environment having a temperature of 25±3° C. to obtaina positive electrode having a positive electrode mixed material layerdensity of 3.40 g/cm³. The positive electrode was subsequently left inan environment having a temperature of 25±3° C. and a relative humidityof 50±5% for 1 week.

<Production of Lithium Ion Secondary Battery>

The negative electrode, positive electrode, and separator were used toproduce a wound cell (discharge capacity equivalent to 520 mAh) and werearranged inside aluminum packing. The inside of the aluminum packing wassubsequently filled with LiPF₆ solution of 1.0 M in concentration(solvent: mixed solvent of ethylene carbonate (EC)/diethyl carbonate(DEC)=3/7 (volume ratio); additive: containing 2 volume % (solventratio) of vinylene carbonate) as an electrolyte solution. The aluminumpacking was then closed by heat sealing at a temperature of 150° C. totightly seal an opening of the aluminum packing, and thereby produce alithium ion secondary battery. This lithium ion secondary battery wasused to evaluate cycle characteristics. The result is shown in Table 1.

Example 2

An aqueous solution containing a water-soluble polymer, a waterdispersion containing a particulate polymer, a slurry composition for aheat-resistant layer, a negative electrode, a positive electrode, aseparator, and a lithium ion secondary battery were prepared or producedin the same way as in Example 1 with the exception that in production ofthe aqueous solution containing the water-soluble polymer, the amount ofacrylamide as an amide group-containing monomer was changed to 889.0 g(70.0%), the amount of acrylic acid as an acid group-containing monomerwas changed to 152.4 g (12.0%), and the amount ofN-hydroxyethylacrylamide as a hydroxyl group-containing monomer waschanged to 228.6 g (18.0%). Evaluations were conducted in the samemanner as in Example 1. The results are shown in Table 1.

Example 3

An aqueous solution containing a water-soluble polymer, a waterdispersion containing a particulate polymer, a slurry composition for aheat-resistant layer, a negative electrode, a positive electrode, aseparator, and a lithium ion secondary battery were prepared or producedin the same way as in Example 1 with the exception that in production ofthe aqueous solution containing the water-soluble polymer, the amount ofacrylamide as an amide group-containing monomer was changed to 825.5 g(65.0%), the amount of acrylic acid as an acid group-containing monomerwas changed to 139.7 g (11.0%), and the amount ofN-hydroxyethylacrylamide as a hydroxyl group-containing monomer waschanged to 304.8 g (24.0%). Evaluations were conducted in the samemanner as in Example 1. The results are shown in Table 1.

Example 4

An aqueous solution containing a water-soluble polymer, a waterdispersion containing a particulate polymer, a slurry composition for aheat-resistant layer, a negative electrode, a positive electrode, aseparator, and a lithium ion secondary battery were prepared or producedin the same way as in Example 1 with the exception that in production ofthe aqueous solution containing the water-soluble polymer, the amount ofacrylamide as an amide group-containing monomer was changed to 825.5 g(65.0%), the amount of acrylic acid as an acid group-containing monomerwas changed to 38.1 g (3.0%), and the amount of N-hydroxyethylacrylamideas a hydroxyl group-containing monomer was changed to 406.4 g (32.0%).Evaluations were conducted in the same manner as in Example 1. Theresults are shown in Table 1.

Example 5

An aqueous solution containing a water-soluble polymer, a waterdispersion containing a particulate polymer, a slurry composition for aheat-resistant layer, a negative electrode, a positive electrode, aseparator, and a lithium ion secondary battery were prepared or producedin the same way as in Example 1 with the exception that in production ofthe aqueous solution containing the water-soluble polymer, the amount ofacrylamide as an amide group-containing monomer was changed to 806.45 g(63.5%), the amount of acrylic acid as an acid group-containing monomerwas changed to 215.9 g (17.0%), and the amount ofN-hydroxyethylacrylamide as a hydroxyl group-containing monomer waschanged to 247.65 g (19.5%). Evaluations were conducted in the samemanner as in Example 1. The results are shown in Table 1.

Example 6

An aqueous solution containing a water-soluble polymer, a waterdispersion containing a particulate polymer, a slurry composition for aheat-resistant layer, a negative electrode, a positive electrode, aseparator, and a lithium ion secondary battery were prepared or producedin the same way as in Example 1 with the exception that in production ofthe aqueous solution containing the water-soluble polymer, the amount ofacrylamide as an amide group-containing monomer was changed to 1219.2 g(96.0%), the amount of acrylic acid as an acid group-containing monomerwas changed to 17.78 g (1.4%), and the amount ofN-hydroxyethylacrylamide as a hydroxyl group-containing monomer waschanged to 33.02 g (2.6%). Evaluations were conducted in the same manneras in Example 1. The results are shown in Table 1.

Example 7

An aqueous solution containing a water-soluble polymer, a waterdispersion containing a particulate polymer, a slurry composition for aheat-resistant layer, a negative electrode, a positive electrode, aseparator, and a lithium ion secondary battery were prepared or producedin the same way as in

Example 1 with the exception that in production of the aqueous solutioncontaining the water-soluble polymer, the amount of acrylamide as anamide group-containing monomer was changed to 939.8 g (74.0%), theamount of acrylic acid as an acid group-containing monomer was changedto 203.2 g (16.0%), and the amount of N-hydroxyethylacrylamide as ahydroxyl group-containing monomer was changed to 127.0 g (10.0%).Evaluations were conducted in the same manner as in Example 1. Theresults are shown in Table 1.

Example 8

An aqueous solution containing a water-soluble polymer, a waterdispersion containing a particulate polymer, a slurry composition for aheat-resistant layer, a negative electrode, a positive electrode, aseparator, and a lithium ion secondary battery were prepared or producedin the same way as in Example 1 with the exception that in production ofthe aqueous solution containing the water-soluble polymer, the amount ofacrylamide as an amide group-containing monomer was changed to 939.8 g(74.0%), the amount of acrylic acid as an acid group-containing monomerwas changed to 63.5 g (5.0%), and the amount of N-hydroxyethylacrylamideas a hydroxyl group-containing monomer was changed to 266.7 g (21.0%).Evaluations were conducted in the same manner as in Example 1. Theresults are shown in Table 1.

Example 9

A water dispersion containing a particulate polymer, a slurrycomposition for a heat-resistant layer, a negative electrode, a positiveelectrode, a separator, and a lithium ion secondary battery wereprepared or produced in the same way as in Example 1 with the exceptionthat an aqueous solution containing a water-soluble polymer that wasproduced as described below was used. Evaluations were conducted in thesame manner as in Example 1. The results are shown in Table 1.

<Production of Aqueous Solution Containing Water-Soluble Polymer>

A 10 L septum-equipped flask was charged with 6,335 g of deionized waterand 95 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator. These materials were heated to a temperatureof 40° C., and the inside of the flask was purged with nitrogen gas at aflow rate of 100 mL/min. Next, 939.8 g (74.0%) of acrylamide as an amidegroup-containing monomer, 127.0 g (10.0%) of acrylic acid as an acidgroup-containing monomer, and 203.2 g (16.0%) ofN-hydroxyethylacrylamide as a hydroxyl group-containing monomer weremixed and were injected into the flask by a syringe. Thereafter, 100 gof a 5.0% aqueous solution of ammonium persulfate as a polymerizationinitiator was added into the flask by a syringe, and the reactiontemperature was set to 60° C. Once 2 hours had passed, 50 g of a 5.0%aqueous solution of ammonium persulfate as a polymerization initiatorand 47.5 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator were added in order to further raise thereaction conversion rate. Once a further 2 hours had passed, 50 g of a5.0% aqueous solution of ammonium persulfate as a polymerizationinitiator and 47.5 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator were added. Two hours later, 34 g of a 5%aqueous solution of sodium nitrite as a reaction inhibitor was addedinto the flask and was stirred. Thereafter, the flask was cooled to 40°C. and was converted to an air atmosphere. The pH of the system wasadjusted to 8.0 using 8% lithium hydroxide aqueous solution to therebyyield an aqueous solution containing a water-soluble polymer.

Example 10

A water dispersion containing a particulate polymer, a slurrycomposition for a heat-resistant layer, a negative electrode, a positiveelectrode, a separator, and a lithium ion secondary battery wereprepared or produced in the same way as in Example 1 with the exceptionthat an aqueous solution containing a water-soluble polymer that wasproduced as described below was used. Evaluations were conducted in thesame manner as in Example 1. The results are shown in Table 1.

<Production of Aqueous Solution Containing Water-Soluble Polymer>

A 10 L septum-equipped flask was charged with 6,335 g of deionized waterand 285 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator. These materials were heated to a temperatureof 40° C., and the inside of the flask was purged with nitrogen gas at aflow rate of 100 mL/min. Next, 939.8 g (74.0%) of acrylamide as an amidegroup-containing monomer, 127.0 g (10.0%) of acrylic acid as an acidgroup-containing monomer, and 203.2 g (16.0%) ofN-hydroxyethylacrylamide as a hydroxyl group-containing monomer weremixed and were injected into the flask by a syringe. Thereafter, 300 gof a 5.0% aqueous solution of ammonium persulfate as a polymerizationinitiator was added into the flask by a syringe, and the reactiontemperature was set to 60° C. Once 2 hours had passed, 150 g of a 5.0%aqueous solution of ammonium persulfate as a polymerization initiatorand 142.5 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator were added in order to further raise thereaction conversion rate. Once a further 2 hours had passed, 150 g of a5.0% aqueous solution of ammonium persulfate as a polymerizationinitiator and 142.5 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator were added. Two hours later, 34 g of a 5%aqueous solution of sodium nitrite as a reaction inhibitor was addedinto the flask and was stirred. Thereafter, the flask was cooled to 40°C. and was converted to an air atmosphere. The pH of the system wasadjusted to 8.0 using 8% lithium hydroxide aqueous solution to therebyyield an aqueous solution containing a water-soluble polymer.

Example 11

A water dispersion containing a particulate polymer, a slurrycomposition for a heat-resistant layer, a negative electrode, a positiveelectrode, a separator, and a lithium ion secondary battery wereprepared or produced in the same way as in Example 1 with the exceptionthat an aqueous solution containing a water-soluble polymer that wasproduced as described below was used. Evaluations were conducted in thesame manner as in Example 1. The results are shown in Table 1.

<Production of Aqueous Solution Containing Water-Soluble Polymer>

A 10 L septum-equipped flask was charged with 6,335 g of deionized waterand 66.5 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator. These materials were heated to a temperatureof 40° C., and the inside of the flask was purged with nitrogen gas at aflow rate of 100 mL/min. Next, 939.8 g (74.0%) of acrylamide as an amidegroup-containing monomer, 127.0 g (10.0%) of acrylic acid as an acidgroup-containing monomer, and 203.2 g (16.0%) ofN-hydroxyethylacrylamide as a hydroxyl group-containing monomer weremixed and were injected into the flask by a syringe. Thereafter, 75 g ofa 5.0% aqueous solution of ammonium persulfate as a polymerizationinitiator was added into the flask by a syringe, and the reactiontemperature was set to 60° C. Once 2 hours had passed, 35 g of a 5.0%aqueous solution of ammonium persulfate as a polymerization initiatorand 33.3 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator were added in order to further raise thereaction conversion rate. Once a further 2 hours had passed, 35 g of a5.0% aqueous solution of ammonium persulfate as a polymerizationinitiator and 33.3 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator were added. Two hours later, 34 g of a 5%aqueous solution of sodium nitrite as a reaction inhibitor was addedinto the flask and was stirred. Thereafter, the flask was cooled to 40°C. and was converted to an air atmosphere. The pH of the system wasadjusted to 8.0 using 8% lithium hydroxide aqueous solution to therebyyield an aqueous solution containing a water-soluble polymer.

Example 12

In production of an aqueous solution containing a water-soluble polymer,the amount of acrylamide as an amide group-containing monomer waschanged to 933.45 g (73.5%), the amount of acrylic acid as an acidgroup-containing monomer was changed to 120.65 g (9.5%), and 215.9 g(17.0%) of 2-hydroxyethyl methacrylate was used instead of 203.2 g(16.0%) of N-hydroxyethylacrylamide as a hydroxyl group-containingmonomer. Moreover, the amount of a water dispersion containing aparticulate polymer that was used in production of a slurry compositionfor a heat-resistant layer was changed to 3 parts of solid content. Withthe exception of the above, an aqueous solution containing awater-soluble polymer, a water dispersion containing a particulatepolymer, a slurry composition for a heat-resistant layer, a negativeelectrode, a positive electrode, a separator, and a lithium ionsecondary battery were prepared or produced in the same way as inExample 1. Evaluations were conducted in the same manner as inExample 1. The results are shown in Table 1.

Example 13

In production of an aqueous solution containing a water-soluble polymer,2-hydroxyethyl acrylate was used instead of N-hydroxyethylacrylamide asa hydroxyl group-containing monomer. Moreover, the amount of a waterdispersion containing a particulate polymer that was used in productionof a slurry composition for a heat-resistant layer was changed to 3parts of solid content. With the exception of the above, an aqueoussolution containing a water-soluble polymer, a water dispersioncontaining a particulate polymer, a slurry composition for aheat-resistant layer, a negative electrode, a positive electrode, aseparator, and a lithium ion secondary battery were prepared or producedin the same way as in Example 1. Evaluations were conducted in the samemanner as in Example 1. The results are shown in Table 2.

Example 14

An aqueous solution containing a water-soluble polymer, a slurrycomposition for a heat-resistant layer, a negative electrode, a positiveelectrode, a separator, and a lithium ion secondary battery wereprepared or produced in the same way as in Example 1 with the exceptionthat in production of the slurry composition for a heat-resistant layer,a water dispersion containing a particulate polymer was not added, andthe amount of the aqueous solution containing the water-soluble polymerwas changed to 4 parts of solid content. Evaluations were conducted inthe same manner as in Example 1. The results are shown in Table 2.

Example 15

An aqueous solution containing a water-soluble polymer, a waterdispersion containing a particulate polymer, a slurry composition for aheat-resistant layer, a negative electrode, a positive electrode, aseparator, and a lithium ion secondary battery were prepared or producedin the same way as in Example 1 with the exception that in production ofthe slurry composition for a heat-resistant layer, the amount of thewater dispersion containing the particulate polymer was changed to 1.3parts of solid content. Evaluations were conducted in the same manner asin Example 1. The results are shown in Table 2.

Example 16

An aqueous solution containing a water-soluble polymer, a slurrycomposition for a heat-resistant layer, a negative electrode, a positiveelectrode, a separator, and a lithium ion secondary battery wereprepared or produced in the same way as in Example 1 with the exceptionthat a water dispersion containing a particulate polymer that wasproduced as described below was used. Evaluations were conducted in thesame manner as in Example 1. The results are shown in Table 2.

<Production of Water Dispersion Containing Particulate Polymer>

A reactor including a stirrer was supplied with 70 parts of deionizedwater and 0.5 parts of ammonium persulfate. The gas phase of the reactorwas purged with nitrogen gas and the temperature was raised to 60° C.Meanwhile, a monomer composition was obtained in a separate vessel bymixing 50 parts of deionized water, 0.5 parts of polyoxyethylene laurylether (produced by Kao Corporation; product name: EMULGEN® 120 (EMULGENis a registered trademark in Japan, other countries, or both)) as anemulsifier, 65 parts of 2-ethylhexyl acrylate as a (meth)acrylic acidester monomer, 30 parts of styrene as another monomer, 1.7 parts ofallyl glycidyl ether and 0.3 parts of allyl methacrylate ascross-linkable monomers, and 3 parts of methacrylic acid as ahydrophilic group-containing monomer.

The monomer composition was continuously added into the reactor over 4hours to carry out polymerization. The reaction was carried out at 70°C. during the continuous addition. Once the continuous addition wascomplete, a further 3 hours of stirring was performed at 80° C. tocomplete the reaction and thereby yield a water dispersion of aparticulate polymer.

The obtained water dispersion of the particulate polymer was cooled to25° C., was subsequently adjusted to pH 8.0 through addition of sodiumhydroxide aqueous solution, and then unreacted monomer was removedtherefrom through introduction of steam. Thereafter, adjustment of solidcontent concentration was performed with deionized water whileperforming filtration using a 200-mesh (opening size: approximately 77μm) screen made of stainless steel to obtain a water dispersion (solidcontent concentration:

40%) containing the particulate polymer.

Example 17

An aqueous solution containing a water-soluble polymer, a slurrycomposition for a heat-resistant layer, a negative electrode, a positiveelectrode, a separator, and a lithium ion secondary battery wereprepared or produced in the same way as in Example 1 with the exceptionthat a water dispersion containing a particulate polymer that wasproduced as described below was used. Evaluations were conducted in thesame manner as in Example 1. The results are shown in Table 2.

<Production of Water Dispersion Containing Particulate Polymer>

A reactor including a stirrer was supplied with 70 parts of deionizedwater, 0.20 parts of polyoxyethylene lauryl ether (produced by KaoCorporation; product name: EMULGEN® 120) as an emulsifier, and 0.5 partsof ammonium persulfate. The gas phase of the reactor was purged withnitrogen gas and the temperature was raised to 60° C. Meanwhile, amonomer composition was obtained in a separate vessel by mixing 50 partsof deionized water, 0.5 parts of polyoxyethylene lauryl ether (producedby Kao Corporation; product name: EMULGEN® 120) as an emulsifier, 70parts of 2-ethylhexyl acrylate as a (meth)acrylic acid ester monomer, 25parts of styrene as another monomer, 1.7 parts of allyl glycidyl etherand 0.3 parts of allyl methacrylate as cross-linkable monomers, and 3parts of methacrylic acid as a hydrophilic group-containing monomer.

The monomer composition was continuously added into the reactor over 4hours to carry out polymerization. The reaction was carried out at 70°C. during the continuous addition. Once the continuous addition wascomplete, a further 3 hours of stirring was performed at 80° C. tocomplete the reaction and thereby yield a water dispersion of aparticulate polymer.

The obtained water dispersion of the particulate polymer was cooled to25° C., was subsequently adjusted to pH 8.0 through addition of sodiumhydroxide aqueous solution, and then unreacted monomer was removedtherefrom through introduction of steam. Thereafter, adjustment of solidcontent concentration was performed with deionized water whileperforming filtration using a 200-mesh (opening size: approximately 77μm) screen made of stainless steel to obtain a water dispersion (solidcontent concentration: 40%) containing the particulate polymer.

Example 18

An aqueous solution containing a water-soluble polymer, a waterdispersion containing a particulate polymer, a slurry composition for aheat-resistant layer, a negative electrode, a positive electrode, aseparator, and a lithium ion secondary battery were prepared or producedin the same way as in Example 1 with the exception that in production ofthe slurry composition for a heat-resistant layer, barium sulfateparticles (produced by Takehara Kagaku Kogyo Co., Ltd.; product name:TS-3; volume-average particle diameter: 0.5 μm) were used instead ofalumina particles as non-conductive inorganic particles. Evaluationswere conducted in the same manner as in Example 1. The results are shownin Table 2.

Comparative Example 1

A water dispersion containing a particulate polymer, a slurrycomposition for a heat-resistant layer, a negative electrode, a positiveelectrode, a separator, and a lithium ion secondary battery wereprepared or produced in the same way as in Example 1 with the exceptionthat an aqueous solution containing a water-soluble polymer that wasproduced as described below was used. Evaluations were conducted in thesame manner as in Example 1. The results are shown in Table 2.

<Production of Aqueous Solution Containing Water-Soluble Polymer>

A 10 L septum-equipped flask was charged with a monomer compositioncontaining 895.0 g (89.5%) of acrylamide and 15.0 g (1.5%) ofdimethylacrylamide as amide group-containing monomers and 90.0 g (9.0%)of acrylic acid as an acid group-containing monomer, and also with 3,650g of deionized water and 50 g of isopropyl alcohol, and the inside ofthe flask was purged with nitrogen gas at a flow rate of 100 mL/min.Next, 70 g of 5% ammonium persulfate aqueous solution and 30 g of 5%sodium bisulfite aqueous solution as polymerization initiators wereadded under stirring, and then the temperature was raised from roomtemperature to 80° C. and was held thereat for 3 hours. Thereafter,1,620 g of deionized water was added, and the pH was adjusted to 8 with10% sodium hydroxide aqueous solution to yield an aqueous solutioncontaining a water-soluble polymer.

Comparative Example 2

An aqueous solution containing a water-soluble polymer, a waterdispersion containing a particulate polymer, a slurry composition for aheat-resistant layer, a negative electrode, a positive electrode, aseparator, and a lithium ion secondary battery were prepared or producedin the same way as in

Example 1 with the exception that in production of the aqueous solutioncontaining the water-soluble polymer, acrylic acid as an acidgroup-containing monomer and N-hydroxyethylacrylamide as a hydroxylgroup-containing monomer were not added, and the amount of acrylamide asan amide group-containing monomer was changed to 1,270 g (100%).Evaluations were conducted in the same manner as in Example 1. Theresults are shown in Table 2.

Comparative Example 3

A water dispersion containing a particulate polymer, a slurrycomposition for a heat-resistant layer, a negative electrode, a positiveelectrode, a separator, and a lithium ion secondary battery wereprepared or produced in the same way as in Example 1 with the exceptionthat an aqueous solution containing a water-soluble polymer that wasproduced as described below was used. Evaluations were conducted in thesame manner as in Example 1. The results are shown in Table 2.

<Production of Aqueous Solution Containing Water-Soluble Polymer>

A 10 L septum-equipped flask was charged with 6,335 g of deionized waterand 95 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator. These materials were heated to a temperatureof 40° C., and the inside of the flask was purged with nitrogen gas at aflow rate of 100 mL/min. Next, 635.0 g (50.0%) of acrylamide and 127.0 g(10.0%) of methacrylamide as amide group-containing monomers, 317.5 g(25.0%) of acrylic acid and 63.5 g (5.0%) of2-acrylamido-2-methylpropane sulfonic acid as acid group-containingmonomers, 63.5 g (5.0%) of 2-hydroxyethyl methacrylate as a hydroxylgroup-containing monomer, and 63.5 g (5.0%) of methacrylonitrile asanother monomer were mixed and were injected into the flask by asyringe. Thereafter, 100 g of a 5.0% aqueous solution of ammoniumpersulfate as a polymerization initiator was added into the flask by asyringe, and the reaction temperature was set to 60° C. Once 2 hours hadpassed, 50 g of a 5.0% aqueous solution of ammonium persulfate as apolymerization initiator and 47.5 g of a 2.0% aqueous solution ofL-ascorbic acid as a polymerization accelerator were added in order tofurther raise the reaction conversion rate. Once a further 2 hours hadpassed, 50 g of a 5.0% aqueous solution of ammonium persulfate as apolymerization initiator and 47.5 g of a 2.0% aqueous solution ofL-ascorbic acid as a polymerization accelerator were added. Two hourslater, 34 g of a 5% aqueous solution of sodium nitrite as a reactioninhibitor was added into the flask and was stirred. Thereafter, theflask was cooled to 40° C. and was converted to an air atmosphere. ThepH of the system was adjusted to 8.0 using 8% lithium hydroxide aqueoussolution.

Comparative Example 4

A water dispersion containing a particulate polymer, a slurrycomposition for a heat-resistant layer, a negative electrode, a positiveelectrode, a separator, and a lithium ion secondary battery wereprepared or produced in the same way as in Example 1 with the exceptionthat an aqueous solution containing a water-soluble polymer that wasproduced as described below was used. Evaluations were conducted in thesame manner as in Example 1. The results are shown in Table 2.

<Production of Aqueous Solution Containing Water-Soluble Polymer>

A 10 L septum-equipped flask was charged with 6,335 g of deionized waterand 95 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator. These materials were heated to a temperatureof 40° C., and the inside of the flask was purged with nitrogen gas at aflow rate of 100 mL/min. Next, 571.5 g (45.0%) of acrylamide as an amidegroup-containing monomer, 317.5 g (25.0%) of acrylic acid as an acidgroup-containing monomer, and 381.0 g (30.0%) ofN-hydroxyethylacrylamide as a hydroxyl group-containing monomer weremixed and were injected into the flask by a syringe. Thereafter, 100 gof a 5.0% aqueous solution of ammonium persulfate as a polymerizationinitiator was added into the flask by a syringe, and the reactiontemperature was set to 60° C. Once 2 hours had passed, 50 g of a 5.0%aqueous solution of ammonium persulfate as a polymerization initiatorand 47.5 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator were added in order to further raise thereaction conversion rate. Once a further 2 hours had passed, 50 g of a5.0% aqueous solution of ammonium persulfate as a polymerizationinitiator and 47.5 g of a 2.0% aqueous solution of L-ascorbic acid as apolymerization accelerator were added. Two hours later, 34 g of a 5%aqueous solution of sodium nitrite as a reaction inhibitor was addedinto the flask and was stirred. Thereafter, the flask was cooled to 40°C. and was converted to an air atmosphere. The pH of the system wasadjusted to 8.0 using 8% lithium hydroxide aqueous solution to therebyyield an aqueous solution containing a water-soluble polymer.

Comparative Example 5

An aqueous solution containing a water-soluble polymer, a waterdispersion containing a particulate polymer, a slurry composition for aheat-resistant layer, a negative electrode, a positive electrode, aseparator, and a lithium ion secondary battery were prepared or producedin the same way as in Example 1 with the exception that in production ofthe aqueous solution containing the water-soluble polymer, the amount ofacrylamide as an amide group-containing monomer was changed to 946.15 g(74.5%), the amount of acrylic acid as an acid group-containing monomerwas changed to 6.35 g (0.5%), and the amount of N-hydroxyethylacrylamideas a hydroxyl group-containing monomer was changed to 317.5 g (25.0%).Evaluations were conducted in the same manner as in Example 1. Theresults are shown in Table 2.

In Tables 1 and 2, shown below:

“AAm” indicates acrylamide unit;

“DMAAm” indicates dimethylacrylamide unit;

“MAAm” indicates methacrylamide unit;

“AA” indicates acrylic acid unit;

“ATBS” indicates 2-acrylamido-2-methylpropane sulfonic acid unit;

“HEAAm” indicates N-hydroxyethylacrylamide unit;

“HEMA” indicates 2-hydroxyethyl methacrylate unit;

“HEA” indicates 2-hydroxyethyl acrylate unit;

“MAN” indicates methacrylonitrile unit;

“BA” indicates n-butyl acrylate unit;

“2EHA” indicates 2-ethylhexyl acrylate unit;

“MAA” indicates methacrylic acid unit;

“AGE” indicates allyl glycidyl ether unit;

“AMA” indicates allyl methacrylate unit;

“AN” indicates acrylonitrile unit;

“ST” indicates styrene unit;

“Al₂O₃” indicates alumina particles; and

“BaSO₄” indicates barium sulfate particles.

TABLE 1 Example Example Example Example Example 1 2 3 4 5 Slurry BinderWater- Amide group- Type AAm AAm AAm AAm AAm composition compositionsoluble containing Proportional 74  70  65  65   63.5 polymer monomerunit content [mass %] Type — — — — — Proportional — — — — — content[mass %] Acid group- Type AA AA AA AA AA containing Proportional 10  12 11  3 17  monomer unit content [mass %] Type — — — — — Proportional — —— — — content [mass %] Hydroxyl Type HEAAm HEAAm HEAAm HEAAm HEAAmgroup- Proportional 16  18  24  32   19.5 containing content monomerunit [mass %] Other Type — — — — — monomer unit Proportional — — — — —content [mass %] Hydroxyl group/acid group   1.00   0.94   1.37   6.68  0.72 molar ratio Weight-average molecular 500 × 10³ 500 × 10³ 500 ×10³ 500 × 10³ 500 × 10³ weight Content [parts by mass] 2 2 2 2 2Particulate (Meth)acrylic Type BA BA BA BA BA polymer acid esterProportional  94.2  94.2  94.2  94.2  94.2 monomer unit content [mass %]Hydrophilic Type MAA MAA MAA MAA MAA group- Proportional 2 2 2 2 2containing content monomer unit [mass %] Cross- Type AGE AGE AGE AGE AGElinkable Proportional   1.5   1.5   1.5   1.5   1.5 monomer unit content[mass %] Type AMA AMA AMA AMA AMA Proportional   0.3   0.3   0.3   0.3  0.3 content [mass %] Other Type AN AN AN AN AN monomer unitProportional 2 2 2 2 2 content [mass %] Glass-transition temperature−40  −40  −40  −40  −40  [° C.] Volume-average particle   0.36   0.36  0.36   0.36   0.36 diameter [μm] Content [parts by mass] 4 4 4 4 4Non-conductive Type Al₂O₃ Al₂O₃ Al₂O₃ Al₂O₃ Al₂O₃ inorganic particlesContent [parts by mass] 100  100  100  100  100  Evaluation Dispersionstability A A A A B Coatability A A A B A Heat shrinkage resistance A BB B B Close adherence A A A B A Cycle characteristics A A A A A ExampleExample Example Example 6 7 8 9 Slurry Binder Water- Amide group- TypeAAm AAm AAm AAm composition composition soluble containing Proportional96  74  74  74  polymer monomer unit content [mass %] Type — — — —Proportional — — — — content [mass %] Acid group- Type AA AA AA AAcontaining Proportional   1.4 16  5 10  monomer unit content [mass %]Type — — — — Proportional — — — — content [mass %] Hydroxyl Type HEAAmHEAAm HEAAm HEAAm group- Proportional   2.6 10  21  16  containingcontent monomer unit [mass %] Other Type — — — — monomer unitProportional — — — — content [mass %] Hydroxyl group/acid group   1.16  0.39   2.63   1.00 molar ratio Weight-average molecular 500 × 10³ 500× 10³ 500 × 10³ 1200 × 10³ weight Content [parts by mass] 2 2 2 2Particulate (Meth)acrylic Type BA BA BA BA polymer acid esterProportional  94.2  94.2  94.2  94.2 monomer unit content [mass %]Hydrophilic Type MAA MAA MAA MAA group- Proportional 2 2 2 2 containingcontent monomer unit [mass %] Cross- Type AGE AGE AGE AGE linkableProportional   1.5   1.5   1.5   1.5 monomer unit content [mass %] TypeAMA AMA AMA AMA Proportional   0.3   0.3   0.3   0.3 content [mass %]Other Type AN AN AN AN monomer unit Proportional 2 2 2 2 content [mass%] Glass-transition temperature −40  −40  −40  −40  [° C.]Volume-average particle   0.36   0.36   0.36   0.36 diameter [μm]Content [parts by mass] 4 4 4 4 Non-conductive Type Al₂O₃ Al₂O₃ Al₂O₃Al₂O₃ inorganic particles Content [parts by mass] 100  100  100  100 Evaluation Dispersion stability B B A A Coatability B B B B Heatshrinkage resistance A A A A Close adherence B A B A Cyclecharacteristics A A A A Example Example Example 10 11 12 Slurry BinderWater- Amide group- Type AAm AAm AAm composition composition solublecontaining Proportional 74  74   73.5 polymer monomer unit content [mass%] Type — — — Proportional — — — content [mass %] Acid group- Type AA AAAA containing Proportional 10  10    9.5 monomer unit content [mass %]Type — — — Proportional — — — content [mass %] Hydroxyl Type HEAAm HEAAmHEMA group- Proportional 16  16  17  containing content monomer unit[mass %] Other Type — — — monomer unit Proportional — — — content [mass%] Hydroxyl group/acid group   1.00   1.00   0.99 molar ratioWeight-average molecular 280 × 10³ 1800 × 10³ 500 × 10³ weight Content[parts by mass] 2 2 2 Particulate (Meth)acrylic Type BA BA BA polymeracid ester Proportional  94.2  94.2  94.2 monomer unit content [mass %]Hydrophilic Type MAA MAA MAA group- Proportional 2 2 2 containingcontent monomer unit [mass %] Cross- Type AGE AGE AGE linkableProportional   1.5   1.5   1.5 monomer unit content [mass %] Type AMAAMA AMA Proportional   0.3   0.3   0.3 content [mass %] Other Type AN ANAN monomer unit Proportional 2 2 2 content [mass %] Glass-transitiontemperature −40  −40  −40  [° C.] Volume-average particle   0.36   0.36  0.36 diameter [μm] Content [parts by mass] 4 4 3 Non-conductive TypeAl₂O₃ Al₂O₃ Al₂O₃ inorganic particles Content [parts by mass] 100  100 100  Evaluation Dispersion stability A A A Coatability A B A Heatshrinkage resistance B A B Close adherence A A A Cycle characteristics AA B

TABLE 2 Example Example Example Example Example 13 14 15 16 17 SlurryBinder Water- Amide group- Type AAm AAm AAm AAm AAm compositioncomposition soluble containing Proportional 74  74 74  74 74 polymermonomer unit content [mass %] Type — — — — — Proportional — — — — —content [mass %] Acid group- Type AA AA AA AA AA containing Proportional10  10 10  10 10 monomer unit content [mass %] Type — — — — —Proportional — — — — — content [mass %] Hydroxyl Type HEA HEAAm HEAAmHEAAm HEAAm group- Proportional 16  16 16  16 16 containing contentmonomer unit [mass %] Other Type — — — — — monomer unit Proportional — —— — — content [mass %] Hydroxyl group/acid group   0.99    1.00   1.00   1.00    1.00 molar ratio Weight-average molecular 500 × 10³ 500 × 10³500 × 10³ 500 × 10³ 500 × 10³ weight Content [parts by mass] 2  4 2  2 2 Particulate (Meth)acrylic Type BA — BA 2EHA 2EHA polymer acid esterProportional  94.2 —  94.2 65 70 monomer unit content [mass %]Hydrophilic Type MAA — MAA MAA MAA group- Proportional 2 — 2  3  3containing content monomer unit [mass %] Cross- Type AGE — AGE AGE AGElinkable Proportional   1.5 —   1.5   1.7   1.7 monomer unit content[mass %] Type AMA — AMA AMA AMA Proportional   0.3 —   0.3   0.3   0.3content [mass %] Other Type AN — AN ST ST monomer unit Proportional 2 —2 30 25 content [mass %] Glass-transition temperature −40  — −40  −25 −30  [° C.] Volume-average particle   0.36 —   0.36    0.31    0.18diameter [μm] Content [parts by mass] 3 —   1.3  4  4 Non-conductiveType Al₂O₃ Al₂O₃ Al₂O₃ Al₂O₃ Al₂O₃ inorganic particles Content [parts bymass] 100  100  100  100  100  Evaluation Dispersion stability A A A A ACoatability A A A A A Heat shrinkage resistance B A A A A Closeadherence A B B A A Cycle characteristics B A A A B Example ComparativeComparative Comparative 18 Example 1 Example 2 Example 3 Slurry BinderWater- Amide group- Type AAm AAm AAm AAm composition composition solublecontaining Proportional 74   89.5 100  50  polymer monomer unit content[mass %] Type — DMAAm — MAAm Proportional —   1.5 — 10  content [mass %]Acid group- Type AA AA — AA containing Proportional 10  9 — 25  monomerunit content [mass %] Type — — — ATBS Proportional — — — 5 content [mass%] Hydroxyl Type HEAAm — — HEMA group- Proportional 16  — — 5 containingcontent monomer unit [mass %] Other Type — — — MAN monomer unitProportional — — — 5 content [mass %] Hydroxyl group/acid group   1.00 ——   0.10 molar ratio Weight-average molecular 500 × 10³ 360 × 10³ 500 ×10³ 1000 × 10³ weight Content [parts by mass] 2 2 2 2 Particulate(Meth)acrylic Type BA BA BA BA polymer acid ester Proportional  94.2 94.2  94.2  94.2 monomer unit content [mass %] Hydrophilic Type MAA MAAMAA MAA group- Proportional 2 2 2 2 containing content monomer unit[mass %] Cross- Type AGE AGE AGE AGE linkable Proportional   1.5   1.5  1.5   1.5 monomer unit content [mass %] Type AMA AMA AMA AMAProportional   0.3   0.3   0.3   0.3 content [mass %] Other Type AN ANAN AN monomer unit Proportional 2 2 2 2 content [mass %]Glass-transition temperature −40  −40  −40  −40  [° C.] Volume-averageparticle   0.36   0.36   0.36   0.36 diameter [μm] Content [parts bymass] 4 4 4 4 Non-conductive Type BaSO₄ Al₂O₃ Al₂O₃ Al₂O₃ inorganicparticles Content [parts by mass] 100  100  100  100  EvaluationDispersion stability A C C C Coatability A C C C Heat shrinkageresistance A B B C Close adherence A A C A Cycle characteristics A A B AComparative Comparative Example 4 Example 5 Slurry Binder Water- Amidegroup- Type AAm AAm composition composition soluble containingProportional 45   74.5 polymer monomer unit content [mass %] Type — —Proportional — — content [mass %] Acid group- Type AA AA containingProportional 25    0.5 monomer unit content [mass %] Type — —Proportional — — content [mass %] Hydroxyl Type HEAAm HEAAm group-Proportional 30  25  containing content monomer unit [mass %] Other Type— — monomer unit Proportional — — content [mass %] Hydroxyl group/acidgroup   0.75   31.29 molar ratio Weight-average molecular 1000 × 10³ 500× 10³ weight Content [parts by mass] 2 2 Particulate (Meth)acrylic TypeBA BA polymer acid ester Proportional  94.2  94.2 monomer unit content[mass %] Hydrophilic Type MAA MAA group- Proportional 2 2 containingcontent monomer unit [mass %] Cross- Type AGE AGE linkable Proportional  1.5   1.5 monomer unit content [mass %] Type AMA AMA Proportional  0.3   0.3 content [mass %] Other Type AN AN monomer unit Proportional2 2 content [mass %] Glass-transition temperature −40  −40  [° C.]Volume-average particle   0.36   0.36 diameter [μm] Content [parts bymass] 4 4 Non-conductive Type Al₂O₃ Al₂O₃ inorganic particles Content[parts by mass] 100  100  Evaluation Dispersion stability C ACoatability B C Heat shrinkage resistance C B Close adherence A C Cyclecharacteristics A B

It can be seen from Tables 1 and 2 that it was possible to form a slurrycomposition having excellent dispersion stability and coatability and aheat-resistant layer having excellent heat shrinkage resistance inExamples 1 to 18 in which the used binder composition contained awater-soluble polymer that included an amide group-containing monomerunit, an acid group-containing monomer unit, and a hydroxylgroup-containing monomer unit and in which the proportional contents ofthe amide group-containing monomer unit and the acid group-containingmonomer unit were within specific ranges. It can also be seen that theheat-resistant layers of Examples 1 to 18 had excellent close adherencewith a substrate and could cause a secondary battery to displayexcellent cycle characteristics.

On the other hand, it can be seen that dispersion stability andcoatability of a slurry composition could not be sufficiently ensured inComparative Example 1 in which the used binder composition contained awater-soluble polymer that only included an amide group-containingmonomer unit and an acid group-containing monomer unit.

It can also be seen that dispersion stability and coatability of aslurry composition could not be sufficiently ensured and aheat-resistant layer having excellent close adherence with a substratecould not be formed in Comparative Example 2 in which the used bindercomposition contained a water-soluble polymer that only included anamide group-containing monomer unit.

It can also be seen that dispersion stability and coatability of aslurry composition could not be sufficiently ensured and aheat-resistant layer having excellent heat shrinkage resistance couldnot be formed in Comparative Example 3 in which the used bindercomposition contained a water-soluble polymer in which the proportionalcontents of an amide group-containing monomer unit and an acidgroup-containing monomer unit were outside of the specific ranges.

It can also be seen that dispersion stability of a slurry compositioncould not be sufficiently ensured and a heat-resistant layer havingexcellent heat shrinkage resistance could not be formed in ComparativeExample 4 in which the used binder composition contained a water-solublepolymer in which the proportional contents of an amide group-containingmonomer unit and an acid group-containing monomer unit were outside ofthe specific ranges. It can also be seen that coatability of a slurrycomposition could not be sufficiently ensured and a heat-resistant layerhaving excellent close adherence with a substrate could not be formed inComparative Example 5 in which the used binder composition contained awater-soluble polymer in which the proportional content of an acidgroup-containing monomer unit was outside of the specific range.

INDUSTRIAL APPLICABILITY

According to the present disclosure, it is possible to provide a bindercomposition for a non-aqueous secondary battery heat-resistant layerwith which it is possible to produce a slurry composition for anon-aqueous secondary battery heat-resistant layer that has excellentdispersion stability and coatability and that can form a heat-resistantlayer for a non-aqueous secondary battery having excellent heatshrinkage resistance.

Moreover, according to the present disclosure, it is possible to providea slurry composition for a non-aqueous secondary battery heat-resistantlayer that has excellent dispersion stability and coatability and thatcan form a heat-resistant layer for a non-aqueous secondary batteryhaving excellent heat shrinkage resistance.

Furthermore, according to the present disclosure, it is possible toprovide a heat-resistant layer for a non-aqueous secondary battery thathas excellent heat shrinkage resistance and a non-aqueous secondarybattery that includes this heat-resistant layer.

1. A binder composition for a non-aqueous secondary batteryheat-resistant layer comprising a water-soluble polymer and water,wherein the water-soluble polymer includes an amide group-containingmonomer unit, an acid group-containing monomer unit, and a hydroxylgroup-containing monomer unit, and proportional content of the amidegroup-containing monomer unit in the water-soluble polymer is not lessthan 63 mass % and not more than 98 mass % and proportional content ofthe acid group-containing monomer unit in the water-soluble polymer isnot less than 1 mass % and not more than 20 mass %.
 2. The bindercomposition for a non-aqueous secondary battery heat-resistant layeraccording to claim 1, wherein proportional content of the hydroxylgroup-containing monomer unit in the water-soluble polymer is not lessthan 1 mass % and not more than 25 mass %.
 3. The binder composition fora non-aqueous secondary battery heat-resistant layer according to claim1, wherein the hydroxyl group-containing monomer unit is a hydroxylgroup-containing (meth)acrylamide monomer unit.
 4. The bindercomposition for a non-aqueous secondary battery heat-resistant layeraccording to claim 1, wherein a molar ratio of proportional content ofthe hydroxyl group-containing monomer unit relative to proportionalcontent of the acid group-containing monomer unit in the water-solublepolymer is 0.70 or more.
 5. The binder composition for a non-aqueoussecondary battery heat-resistant layer according to claim 1, wherein thewater-soluble polymer has a weight-average molecular weight of not lessthan 200,000 and not more than 2,000,000.
 6. The binder composition fora non-aqueous secondary battery heat-resistant layer according to claim1, further comprising a particulate polymer.
 7. A slurry composition fora non-aqueous secondary battery heat-resistant layer comprising:non-conductive inorganic particles; and the binder composition for anon-aqueous secondary battery heat-resistant layer according to claim 1.8. A heat-resistant layer for a non-aqueous secondary battery formedusing the slurry composition for a non-aqueous secondary batteryheat-resistant layer according to claim
 7. 9. A non-aqueous secondarybattery comprising the heat-resistant layer for a non-aqueous secondarybattery according to claim 8.